I'm torn on this one, unfortunately. On the one hand, this is an excellent game -- the graphics are extremely well done and the controls are excellent. While it is a little repetitive, this is a very respectable dungeon-crawling action game, similar in tone to the very famous (and much-loved) Diablo series. If you liked Dungeon Hunter 2, you'll be glad to see that the series has abandoned arenas for an actual story again, and I think all three of the game's classes are well-balanced and fun to play.
That's all fine and dandy, but the issue here isn't with the game, it's with the business model. Dungeon Hunter 4 is a freemium title, and I'd go so far as to say it's viciously freemium. It's up to you what the most annoying of its many in-app purchase tricks are, but they include putting a timer on potions so that you have to wait or pay to use them frequently, teasing the player with better items for sale right there in your own personal inventory, or making you wait in real time (or pay, again) for item upgrades and crafting. One of these ideas might not be so bad, but including all of them means that a good quarter of your time in Dungeon Hunter 4 is taken up with the game tempting you to spend money, rather than just enjoying your time in the game's virtual world.
It's up to you whether that works or not. Personally, I like Dungeon Hunter 4 -- I won't spend any money in it, but I get a kick out of the action RPG gameplay, and I can see sitting down for some multiplayer sessions with friends. If everyone who downloaded this game played like me, however (without spending any money at all), then Gameloft would go out of business, or have to fall back on a premium model. So it's up to you -- if you feel this is a worthwhile way to sell games, then by all means, give them your money. If you think making the monetization systems almost as complex as the game itself is a mistake, then it's probably better to move on and try something else. Ridiculous Fishing, for example, is an excellent title that leaves gameplay and monetization completely separate.