You will be hard-pressed to find a game that is both deeply challenging and provides a narrative that makes each loss you take feel like a personal failure. The game does not hold your hand, and you are *forced* to think about each strategic decision you make.
The remastered editions are beautiful, exquisitely detailed and worth a few multiplayer matches lost due to gawking at the battles. While there are some significant day-1 bugs, GBX and BBI have promised support and the community is heavily involved in scouring the game for any and all necessary improvements.
The classic versions are just as I remember, and they no longer require edits to command line options or registry content to get them to run correctly.
Buy this game. If you love strategy games and you love to THINK, this game is for you.