Before I say what I am going to say... I am a true to heart, die hard, PC gamer, and have been since the beginning... And always will be, but my brother bought a 360, and I have to say... the Halo series is one of the best FPS's ive ever played. Its so polished, it looks amazing (even for a console), the sounds are spectacular, and the studio really listens to its consumer base... Flame suit on, but other than CS Source and 1.6, as well as the Battlefield series, I really do enjoy Halo.
At first I really couldn't get around to upgrading from bf2 to bfbc2... (well not upgrading, but more like moving on), but lately with the looming release of BF3, I have been trying to catch up, and I really do enjoy BFBC2. Counter Strike... Nuff said, easily "THE" FPS of like all time, and i think any PC gamer will give it credit for its revolutionary game play mechanics and building a game with the consumer in mind
All just my opinion, go ahead and disagree, but no one will ever agree to just about everything. Feel free to flame on, but idc, its my honest opinion on the FPS world (though I am more of a MMO, strategy kind of guy, with an occasional need to change it up with FPSs). BTW the story line in Halo is also fantastic in my opinion, its well polished and follows its books and pre-written lore to the T. Which is important with a heavily story driven game such as Halo. Great MP and SP alike, both are enjoyable and carry a lot of replay incentive.