When people talk about raiding in Wrath of the Lich King, a lot of the complaints often boil down to Naxxramas. It was out too long before a new tier of raid content, the fights were too dumbed down from the original raid's difficulty and it was too easy. It was an unimaginative way for Blizzard to cut corners and save time developing Wrath. While I'm personally critical of Naxxramas as a raid instance in its current implementation, let's look at these points and discuss their validity.
- Naxxramas was out too long before a new tier of raid content. This one's pretty subjective, but we can consider two factors. First, Naxx went live with Wrath's release in November 2008, alongside Malygos (Eye of Eternity) and Sartharion (Obsidian Sanctum). Malygos' itemization was half a tier superior to that of Naxx itself, so that items that dropped in the 10-man version of Eye of Eternity were equivalent to those that dropped in 25-man Naxx. Malygos-25 drops were superior to anything that dropped in Naxxramas off anyone but Kel'Thuzad himself. So while we could say that this entire tier of raiding lasted from launch until the release of Ulduar in April 2009, it's unfair to single out Naxxramas as the sole offender. Furthermore, Trial of the Crusader launched in August 2009, meaning that Ulduar's duration as the top tier of raiding was only a month shorter than that of Naxxramas/EoE/OS. Are we really arguing that the 20 bosses of those combined three raids had so much less raiding potential that an extra month or so wasn't at least subjectively justifiable?
- The fights were too dumbed down from the original raid difficulty; it was too easy. Not only is this reason extremely subjective, it also somewhat misses the point. Naxxramas-40 was the ultimate raid of vanilla WoW, the end of the road. It was in effect the blueprint for Sunwell and ICC. The fights were the cutting edge of raid encounter design, the gear the ultimate in vanilla's itemization. Compare that tanking sword with BC blue drops for an idea of just how good Naxxramas-40 itemization was -- you could walk into Karazhan in Naxxramas-40 gear and lose nothing, while if you walked into Naxxramas-10/25 in Sunwell gear, you were in fact missing out on blue drops from instances that were actually superior to Sunwell gear. (You could still run Naxx 10/26 in Sunwell gear; it just wasn't as crushingly superior to leveling gear as Naxx-40 gear was.) Now, asking the introductory raid for Wrath of the Lich King to be as difficult as the final raid of original World of Warcraft is not only absurd, I'm not even sure it's feasible. Naxxramas-40 had 40 people in it. You could see fights that demanded seven or eight tanks to complete. Given the constraints to adapt the ultimate 40-man raid experience into one that could be experienced by 10 or 25 players, Naxxramas is in fact a triumph of fidelity from its orginal format. It made changes only when doing so was necessary either from a story line perspective (i.e., Mograine can't be there because he's canonically somewhere else) or because asking two tanks to do what eight once did, or throwing all that healing pressure once handled by seven or eight healers onto three, would be absurd.
- Converting Naxxramas to a 10/25-man raid was an unimaginative way for Blizzard to save time developing Wrath. This, to me, seems at once the most reasonable and yet most inaccurate criticism of Naxxramas 10/25. It's the most reasonable because it's easy to see why people would think this. It is, after all, fundamentally the same raid space, the same models and as close as they could get to the original fights. Just pick it up, plop it in Northrend and tune the fights for different levels and numbers, and we're good to go, right? No way. First off, it's clear that an enormous amount of modeling and itemization work was done before the decision to use Naxxramas as a raid in Wrath. From the item names and the design of the instances in question (extra portals, huge hallways), we can speculate about where and what those raids would have been, but it's clear that choosing to adapt Naxxramas did little, if anything, to save anyone any work. Heck, making the decision to turn Naxx into a 10/25-man raid for characters 20 levels higher than its original design was, if anything, a ludicrous amount of work for the developers. Compare just the differences between Loatheb in his current form and his original form. Adapting a fight that not only had 40 players to 10/25, but also had consumables mechanics and a different raid comp (no shamans and paladins in the same raid, no death knights of any kind) requires so much work that it would actually be easier to start from scratch with an entirely new raid rather than trying to hold onto the feel of the old encounter. As to the imagination required, it's hard to dispute that the reason was much less "we can't think of anything" (since clearly they had thought of at least two other raids that Naxx displaced) and much more the stated reason of letting people get to see a raid few saw in vanilla.
Furthermore, while the developers did do some masterful work converting Naxx to a level 80 raid, the place where the conversion feels the most strain isn't at all in moving from level 60 to 80, but rather in moving from 40 people to a variable size of 10 or 25. It is my belief that it is the variability of raid size at 80 that is the culprit. Frankly, 10-man raids work best when designed for 10 people, and 25-man raids work best when designed for 25. The challenge of changing a 40-man to one of these two raid sizes is already pretty severe, but to then have to make a raid that works in either size at once is adding another hurdle to jump. Some raids feel best in one size over another. (To my mind, ICC-10 feels stronger, better designed and more epic at times than ICC-25, while the opposite is true for Ulduar -- your mileage may vary.) But I do think that in most cases, Blizzard has done well to design raids in Wrath for both sizes. However, in Naxx, I am of the opinion that scaling down to 25 or 10 was hard enough, and then having to be capable of flipping the switch between those two sizes was almost insurmountable.
Additionally (and to some degree, this is an unavoidable consequence of updating content from two expansions ago), Naxxramas just doesn't hold up visually compared to Wrath's other raids, especially big tent peg raids like Ulduar or ICC. Don't get me wrong, Naxx is a gorgeous raid instance, the absolute best of the best we had to experience in original raiding. But after not only seeing innovations and improvement in BC raids like Tempest Keep, SSC, Hyjal, BT and Sunwell but then moving into entirely new territory with Wrath, Naxx looks like what it is: an old raid. The revamped tier 7 gear often looks inferior to its original tier 3 models (who would dispute that Dreadnaught looked better than Heroic or Valorous Dreadnaught, as an example), and the original weapon models available through Naxx-10 don't even try to really update the old models (a wise choice on their part). To my eyes, this wasn't really as much an issue until Ulduar dropped, with its astonishing art design, absolutely making Naxxramas look older and more tired just by existing.
Finally, there were the achievements. While achievements have improved over the course of the Wrath raid cycle, in my opinion it would not be unfair to say that the way they were implemented in Naxxramas was often completely shoehorned into the instance. The Immortal/Undying was an absolutely grueling test not only of your raid and its ability but also whether or not everyone managed to have a completely flawless internet connection for every single fight. Frankly, with drake lust the way it was back then, those two achievements ended up with more swearing and tears due to stories like, "We had a perfect Immortal run until one of the healers DCed on Heigan," or what have you.
In the end, I'd argue that Naxx-10/25 was in fact an absolute feat of raid design and game design that did exactly what it was intended to do: provide an introductory raid experience with a great deal of variety, update the absolute pinnacle of old WoW raiding to a new raid paradigm, and give both old players and new ones a chance to experience a great bit of classic raiding most had never seen. Unfortunately, it was asked to do so much that there was really no way it could do it all perfectly and had problems balancing the 10- and 25-man formats. (Later raids designed with this paradigm more firmly in mind would improve on it.) It couldn't help the fact that it looked and sounded and played exactly like what it was, namely, content from more than two years previous to Wrath of the Lich King.