First on performances: On my modest rig, the game runs really smoothly on DX11 with everything maxed out except on option that I don't recall. The game, IMO, is gorgeous (DX11 must help at that), the landscapes and water details are really nice in a way that exploring is fun.
The interface can be weird at first. I've played Civ 1 and 2 extensively and a few hour on Civ IV (which I couldn't get into) and now Civ V (which is my favorite with the first one).
The settlers and workers get a signal when they're doing nothing so we don't forget about them but the other units you just have to think about them...is there an option to tell us when ANY unit is idled?
So far so good, I started my first game yesterday with the Ottomans. Discovered some ancient ruins and defeated 3 barbarians camps so far but I think I attacked a neutral city-state too fast (they pissed me quickly...I protected them from barbarians and a dozen turns later we're no longer friendly?!!?...yeah then eat my flame arrows and spears!!!!!!!). I'm enjoying this game a lot, great buy for fans and new players!