Massively in Moria: Soloing vs. Grouping with the Warden
The Warden actually does quite well in both solo and group situations, but for different reasons.
Soloing
With skills such as Ambush, Careful Step, Forced March and the many protective healing Gambits, soloing as a Warden is quite easy. Both of the new classes were designed to be solo-friendly, and this is especially evident in the way they can go from healing to damage according to the arrangement of skills.
The main point we want to focus on with solo Warden play is single target battles. The Warden is not made to take on four enemies at once. They're made to be scouts who can be agile in the field and precise in their killing (or... demoralizing, if you wish). Despite the fact that the Warden does have effective taunts and threat-stealing abilities, it's their skill that will back up these threats, not their armor. So don't expect to draw aggro and absorb damage like a Guardian. Your role as an off-tank support class allows more flexibilty during battle, but not really enough to take on the entire Flaming Deeps on your own.
Grouping
While these new classes were designed as solo-friendly, don't let that fool you into thinking that the Warden isn't effective in a group as well. Stemming from the fact that it's basically a single-target class, you'll depend on the others in your group to keep threat, deal damage and regain Morale more than you could do on your own. However, you can do all of these things as well.
As far as what you'd have to offer the group, again we've found that other classes shine brighter in particular, specific cases. Yet the Warden is flexible enough to fill in so many different roles that this is their shining point in a group, especially in desperate situations. If your Guardian is down, you can grab aggro until he returns. If your Hunter is down, you can become effective at ranged DPS. If your Minstrel is becoming overworked, you can heal yourself, allowing them to concentrate on those who have no self heals. However, as in that last case, most of the Warden's skills are made to benefit him and only him.