IMO, they are both great games. but either way, you better get used to the gameplay of gears 2 if you're going to continue the series. i highly doubt epic goes back to the gameplay of the first game for gears 3. they'll more than likely just build off of what they have.
now that the matchmaking seems to have gotten a little better, the only thing that really bothers me currently about gears 2 is the chainsaw. it's still borderline impossible to escape from people running around the map holding the B button.