Hello.
I cannot remember much about C&C Generals, but off the top of my head I would say Act of War is more realistic than Generals, has a better story and more action oriented FMVs.
When I say higher level of realism, I mean you have Fat-vees which perform very much like humvees. They are fast and ram infantry easily, but at the same time one hit by a rocket and BOOM. Snipers take out infantry in one shot. Infantry can ambush behind terrain to do more damage. The Tunguska AAA not only takes down aircraft, but also works well against infantry. Bradley can carry few troops with moderate fire power. Basically the game's units perform how I would expect them to in real life, but take this with a grain of salt as all my knowledge comes from books movies and other games.
There are also unrealistic things about Act of War. Heavily armed exoskeletons, stealth tanks and severely short sighted helicopters to name a few.
The single-player story of Act of War: Direct Action is a very big plus point.
The same way how Rainbow Six had Tom Clancy to help write the story for the game, Act of War: Direct Action had Dale Brown to help with the story. One difference though, where Rainbow Six the book's story is better than the game's story, for Act of War, the game's story is far better than the actual book of the same name. Act of War still ranks top on my website for having the best story out of all RTSs I have played. High Treason's story was good, but not as good as Direct Action's.
FMVs in Act of War is great. I cannot remember if Generals had FMVs, but I reckon Act of War's FMVs are better than C&C3 Tiberium Wars.
Act of War plays much faster than C&C Generals as I remember it. I find that my troops tend to die very quickly in Act of War. Not as fast as Dawn of War, but still fast.
There are three very different sides in Act of War. This I would say is on par with Generals.
Infantry plays a very important role in Act of War. Infantry must be used to capture other infantry units to be POWs which is an important source of income for Act of War. Gives a very good reason to try and rescue that chopper pilot that crashed on the front lines.
One thing I did like about Generals over Act of War is the balanced difficulty of the single-player campaign. Act of War: Direct Action's campaign was way too easy on the highest difficulty. Then High Treason's campaign was way too difficult on the easiest setting.
I have not played Generals multiplayer, but the few games of Act of War online was a lot of fun. Once again, it plays quite fast. Sent a bunch of tanks to an area, went back to manage my base, went back to find all my tanks taken out by a few hidden AT infantry.
I don't have C&C Generals ranked on my website, but if you are interested, here is
my page that compares Act of War and C&C 3.
Hope that helps.
I absolutely love Act of War.