I'm quite sure that Power Grid is probably my 3rd favourite board game of all time. I've bought 3 expansions for it and I just love it (although the Benelux expansion is POUBELLE). It's a game that you have to be in the 'mood' to play cuz it's quite math-heavy. In fact, in our play groups, we authorize the use of a calculator to speed up gameplay which can totally jam up during auctions (best auction game of all time, btw).
I've come to recently appreciate this game on another level as my fiancee made some new friends who don't really speak English and not much French either. Language barrier was a big problem between us and I taught them Puerto Rico which went well but I think Power Grid was probably the way to go since there are absolutely no words at all in this game. Plus, as bad as the rule book is, it is some of the easiest rules to grasp ever.
As long as you don't have 5-6 players, it's a very fast game as well. Most of our games run 2 hours. When you throw in 6 players, it can get daunting in length though.
Lots of player interaction through the bidding auction process of acquiring power plants which is fun. You can really screw other players by over-buying resources which can leave some feeling sour.
It's also a beautiful game. Lots of colours, gorgeous play pieces, cards, boards. I highly recommend the new power plant expansion pack. Replace your old power plants with the new ones and it's like playing a new game!
One of the WEIRDEST things about this game is that although I think it's a perfectly designed game and well-balanced, I don't have nearly as much fun playing this as I do Agricola or Puerto Rico. So it's very rarely one I suggest to play. It's fun 2-player as well though which is good when you have a gaming significant-other.
Power Grid is a great game. The phases cohere together very nicely. It's surprisingly fun for such a methodical system and dry theme. For me, it scratches the same itch as Acquire but I prefer the implementation of economic processes in this one (out-of-control bidding wars; supply-and-demand based resource market).
This is one of my favorite Euros. I love the economic aspect of the game and how it controls the resources. Better implemented than the similar concept in Supremacy. I also love the artwork for the various powerplants. The math exercise isn't too bad. The marathon aspect is best. Manage when you're going to make your strike.