The GLA haven't been underpowered. If anything they have been made even more of a match against China and the US.
I mean look at the Combat Cycle. Load up some terrorists on some Cycles and boom instant devastation. The Cycle is also one of the few units that is almost all-terrian. The ability for the cycles to just come down over a cliff out of nowhere and suprise you is great. Great for hit and run (espically against Battlemasters). The Cycle is definately a match for almost any units on any of the other teams.
The Battle Bus is another of the evening forces. I mean first you have a humvee (in a way) and then when it gets destroyed you get a building. I mean a great tactic (That I have used on numerous occasions) is poistioning my Buses so that when they get destroyed they create a wall effect. Loaded with RPG troopers, you've got quite a wall. Once again a great evening force for the GLA.
Seriously I have to hand it to EA. I personally say well done to them. When the patches came out (for Normal Gen.) it put many people off playing the GLA. Now EA has realised the problems that have been created. Therefore they fixed it when they made Zero Hour. I like the fact that I can hide my defenses and then pull a force of fully upgraded Maruaders out of nowhere and catch my enemies off guard.
It all comes down to opinion and what you think, but IMO the GLA have been transformed into a force. One that gives the other 2 factions a run for it's money
On the co-op mode I agree. I loved playing the Co-Op YR campaigns and wish it was the same in Generals, but hey no-one is perfect.
Happy Gaming
~Chantillas/Wize