If you get this in a bundle or in a serious sale (80% +), not a bad deal. Otherwise...you are better off with the Ace Patrol games.

I'm on the opposite side; I'll gladly buy it when it is available on GOG. :)

huh?? I played thousands of hours of civ4 and mods, but Civ5 has many improvements and I miss nothing, so I only play that now.

Then we prefer different things. Your improvements are probably my facepalms.

I'd rather play another 1000 hours of Civ 4 than another hour of Civ 5.

Why? Combat is fun now, no more doom, feels more like a real war with frontiers. The civs are finally unique, it is much fun to try them out or master them. The faith system is awesome. The diplomacy is brilliant, the things you can do with denounciations and warmongering are amazing (once you understand how it works, it's not easy,many people complain out of ignorance about this), finally the smaller civs will gang up on the big ones because of this system. The culture policies are numerous, the endgame is less tedious, the turn wait times are much faster.
Apart from the mods, I see no reason to still play Civ4.

Like I said, we must prefer different things in the games. I hated the shallowness of Civ 5, and much prefer the many different routes and strategies one can use in Civ 4, and how competitive the AI can be at the highest levels. People with much more experience than me in Civ 5 say that Deity there is much easier than in Civ 4 (where Deity really is brutal), and that in Civ 5 it's basically "get 4 cities, win". Not quite so in Civ 4.

But again, we must prefer different things in the games. Obviously there is something you like about Civ 5, so great, keep playing that, and meanwhile I'll stay well clear of it.

But it is not shallow, it is much more complex with many more features and more content. That is why I like it more.

Civ 4 and 5 are different games, already the one unit per tile vs. big stacks in Civ 4 make a huge difference. Complexity of features they are certainly on par, Civ 5 could even have more, but it's really difficult to judge about complexity of strategic thinking required. And finally it makes a big difference if you play single player or multi player. The AI in both is usually really bad and relies heavily on cheating. This influence the game and the playing style.

All in all: both deserve to be played, although I prefer Civ 5 which has some very nice scenarios, but then I never really tried one of the many famous total conversion mods for Civ 4. I still need to do it.