I feel I should address some of those complaints because I feel they aren't entirely fair.
It's a common complaint about other Civs, but I've found that they respond in fairly expected ways to your actions. Basically, you have to keep your word and not settle too close to them or else they'll start to distrust you. There's two factors, one, they don't show the diplomatic numbers because it really isn't realistic (both from a real world perspective and from the perspective of playing against a human). Second, they are playing to win, so they'll respond with hostility if you start conquering the world. I've also found that, through animations and tone (with a couple of exceptions), you'll know it when they're angry.
I don't see how research pacts can get you ahead of everyone else, you both get techs out of it.
There are a couple of nice wonders, but a lot are quite boring, which is a shame. I actually like the paintings and quotes. Civ4's videos were something I skipped after the first time (and to be honest, some of them I skipped the first time. They're all extremely predictable. Now if they were Civ2's videos I agree).
Interestingly, they did implement religion (with 8 religions that were different from Civ4 and even considered a religious victory). However, since the AI responds as a human would and is unaffected, they discovered it just felt like you were going through the motions.
They haven't had Ode to Joy for WLTK since Civ2. It was nice back then, but that's a long time to complain about something being missing.
Golden Ages are something good if you can keep it going. I conquered most of the world in my last game and usually ran a -1 happy. I'd say that's a strategy, not an exploit. For large empires, consider that as well. Large empires are good for science and gold. They won't grow, however, and I think you might get production penalties. If you let it get too bad, then your armies lose effectiveness too.
I agree about SMAC. If they improved the AI it would be perfect. However, keep in mind there's no religion, visible AI modifiers, etc either. It also had some flaws (it kept the Civ2 trade system, which I never liked, although I might have warmed up to it with the Civ4 religions system).