Is it heck possible to play Civ V peacefully, the AI constantly declares war on you
I do not find this to be true. I find that when the AI declares war on me, one of the following things has happened:
1) They are an aggressive neighbor and I have a very weak military compared to them.
2) I have made myself thoroughly obnoxious in one of several predictable ways, the most common being that I'm playing that game as a warmonger myself.
If you expand moderately in the early game, then develop your modest empire peacefully, never declaring war on anyone (including city-states) . . . If you either never accept DoFs or, after doing so, always give your friends handouts when they come begging . . . If, despite all this, you keep a strong military with up-to-date tech, on the philosophy of peace through strength . . . then they will leave you alone throughout most, if not all, of the game.
People who complain about the CiV diplomacy system simply don't understand it. I don't fully understand it myself, but I still find it vastly superior to its predecessors.
Subjective viewpoint -- what bhavv said about CiV not being as addictive as Civ IV is not at all true for me. In fact, this is the first game in the series since the original Civ 1 that has had me up until ridiculous hours playing. In many ways, this game has returned to the feel of the original, which was lost for me in the sequels somewhere along the way. Perhaps a part of that is the combat system. While Civ1 allowed stacking just like 2-4 did, only very foolish players would actually do it except to defend cities with, because of the (rather bizarre) rule that if an attack on a stack succeeded, the whole stack died. You tended to spread your attacking units out to keep from losing them all in one lucky/unlucky fight. Whatever the reason, whether it's that or something else, this is by far my favorite in the series.
About the AI being bad at military tactics, that's true, but in fairness it would be a real challenge to develop an AI capable of handling this stuff. When "tactics" meant "compile Stack of Doom and fling it at opponent's city," a game routine could be much more competent than when the system requires actual tactical judgment.