I'd say they are very different. RB1 is great, but campaign missions are just the usual single missions, and the game will spawn a very predictible set of enemies. e.g 2 waves on escort recon missions, balloons and up to 4 planes in balloon busting etc.
Not that its not fun, I love that game. But once you've played a campaign, the missions become fairly predictible. Still, the promotions, and evolution of the aircraft is really well done.
RB2(/3D) campaigns are just mad. In a good way. Theres just so much going on. There will be several flights from your squadron off doing other things, flights from local squadrons off on their own mission, enemies patrolling, bombers coming over, sometimes you see infantry attacks going on on the front. It feels like a real warzone.
As a result it has an epic feel to it. It won't be long before you have these kindof epic missions where you do this, then get jumped by these guys, then bailed out by some friendlies in the area, then have get chased back home, injured and missing your ailerons. No two missions are the same, and it really never feels scripted. Check out the other threads on this forum.
So its hard to fault either choice, but seeing as its not 1992, maybe go for RB3D