http://www.realitymod.com
In a nutshell, it's what BF2 should of been. No dumbing down of the weapons for gameplay purposes, proper squad based play and a slight tinkering of the gameplay to make things a little more exciting at times (flags have to be captured in a specific order, so no lone wolf running off to the other side of the map to capture quiet flags). There's limited sniping kits (normally only 2 per team on a 64 man sever) so you don't get a whole team of campers too.
It's a lot harder than BF2, and as a result the pace is somewhat slower, though the all new maps ensure you're never bored. VOIP is a must, as is joining a squad since certain kits are limited to squads which have a certain amount of members only. Sounds restrictive, but it really brings home how rewarding squad play can be, and 'persuades' you to play as a team rather than lone wolfing.
It's a hefty download at 1.6 gig and you need the BF2 v1.41 patch, but it's well worth it.