Gears 1 is the only MP I spent more than passing time with this generation.
Personally I just think Gears 2 was a step down in almost all respects, but Gears 3 looks like back to form. They've even talked a lot about going back to Gears 1 style in interviews. 2 was too many set pieces, too much on rails, too much scripting, they clearly recognize that. For me Gears is always at its best when it's you in a courtyard, running low on ammo, with two boomers bearing down on you. Those are magical moments. Gears needs to be about courtyards, enemies and weapons not scripted pieces imo.
I popped Gears 1 in the other day to check out the graphics. It looks pretty spartan now in terms of shaders and detail. The back of Marcus head looks really bad too in that down the rifle view. Lots of just ugly there. Gears 3 looks much better. OTOH the detailed enemy character models and ragdoll animation when they get peppered with bullets still look good in Gears 1 even today.