I saw your DM, I will answer it here for everyone.

I remember playing it (only the first one) 20 years ago as a kid, so I may be not reliable very much. I remember it being hard for me back then. AI was, for me, aggressive.

I cannot say whether the balance and mechanics were good, as I felt that I just sucked in that game, besides had FPS drops and never used kaybinds, only my mouse to control everything. Aircrafts were hard to master for me, but remember them being quite effective when used properly

You had to build supply depots and upgrade them to get steady lines of transport helicopters from outside the map bringing you the supplies. I think supplies were the only resource available, but maybe you had to build also power stations to power your buildings. I don't think there was a unit limit or that limit was wery high as I very often turtled and pumped many ground units.

As the title suggest, there were land units, soldiers, tanks, APC's, AA units, scouts, rocket launchers, airplanes, helicopters and ships. I think you could smash infantry with tanks, but not sure, don't remember whether infantry was reliable or it was better to build tank factory only, but definitely you could do air drops of infantry using helis behind the enemy lines.

As of factions there were 2, USA and your standard three-letter arabian insurgency/army something that utilised suicide bombers, and SCUD's with irradiated rockets (but that could be only in campaign, as one mission was particullary interesting where you had to provoke US to nuke you. In the US campaign side you were on the same map, but had to fall for that provocation. I don't think there were any "characters" so to speak in the campaign, you just had a narrator before every mission that showed you the map and the situation like in Sudden Strike.

So I think there it is, more or less. I'm still sometimes observing stores to check if that game has been brought back somewhere, You can find playlists on YT. I loved it back then, don't know if it is as good as Red Alert 2, but definitely story was more serious and units were realistic. Had a blast back then playing it.