Well, I can only comment on Joint Ops as I haven't played Call of Duty.

Joint Ops is very fast paced, and there is a lot of death-by-sniper happening. Some feel that snipers are an abused class, but, in worst cases, it is possible to restrict it via server commands. That said, I don't feel that the proliferation of snipers even comes close to ruining the game for me. It can be frustrating at times, but the nature of the team-focused gameplay far outweighs shortcomings like this. Besides, you quickly learn how to reduce your vulnerability to them (somewhat), and it seems that armies of snipers seem to come and go in waves. Once people start dying from sniping a few times, they change classes and go counter-sniping. Seems to do the trick to restore a little balance.

The teamwork, as we're working on here, makes this game incredibly fun. Well coordinated assaults/defenses, supported by a range of classes, makes for intense and thrilling gameplay... the most enjoyable gaming that I have ever had online.

And as for dying a lot, whether by sniper or not, the medic class allows a player to revive another to full health within a certain time window following their 'death.' The only times this cannot be done are following a headshot (complete death, you can only respawn), and I believe falling great heights, drowning, etc. But most combat damage that I've seen (with the exception of explosives... I imagine they're pretty un-recoverable) can be healed by a friendly medic.

Ultimately, these features, along with the shear size of the maps, and depending on the number of players on the server, singel games can last up to several hours. Sure, you'll probably die a lot, but you get to play *a ton!* Like I said, fast paced, but it's great fun with a tight team.

For more, check the Joint Ops section, as Apophis suggested. In particular, read the thread, Retail - Thoughts? for more concise thoughts.