Absolutely one of the BEST RTS games out there. I've bought this game three times already... In any case, the gameplay is just as innovative now as it was back in... Well, I don't remember. I was literally a kid then. Games are only just now starting to pick up on the complexity and customization that this game brought to the table, and its graphics honestly still look pretty damn good, especially considering its age.
On the note of graphics, on both my hard copy and GOG.com copy, there is widescreen incompatibilities that will crash the game. This is simply because widescreen didn't actually exist when the VooDoo APIs (remember those beasts?) were written. Fixing it is fairly simple though. Look up nGlide, download the driver package and executable, configure and enjoy. Basically what it does is trick that old VooDoo software into thinking it is still in 4:3 while you're running 16:9 or 16:10 formats, plus it'll work with any game that was programed for those old VooDoo GPUs. Mechwarrior 3, here I come!
Gameplay wise, this game is both forgiving and unforgiving. The campaigns are long, and its amongst the few games that allows you to continue the campaign even after losing missions and battles. That's the forgiving part... The unforgiving part is that the game is basically a resource rush, battling relentless and challenging AIs over resources and trying to mine them out and send them back to your main base. While the game gives you plenty of opportunity to achieve your goals, the AI is very intelligent, and will stop at nothing to end you. Failing and/or fumbling battles too much will result in watching your people die in a firey apocalypse, and there won't be jack ♥♥♥♥ you can do about it. That being said, there is a huge number of missions for each campaign, some of which are only available under certain circumstances such as "Lose here..." or "Win there..." or the like.
The game provides a huge variety and complexity in units, weapons, and research, all of which makes for customizable units to a degree unseen in RTS with the exception of maybe Sid Meier's Alpha Centauri. Throughout the game, whether in single or multiplay, you're have to balance cost, quality, quantity, and power for your units, weapons, and research, and rushing tech is much more complex than you'd see in other RTS like StarCraft or Dawn of War. Overall, each faction has a huge variety of units and lacks the over-simplified "this unit counters this" dynamic that seems to be so prevalent in RTS these days.
If this game has shortcoming at all, and obviously I don't think it does, it would be in its story. The game runs on a simple premise, described in the manual, box, and on the Steam page, of "The world was nuked to death by UCS Robots, and its orbit was disrupted enough that it's orbit has started to destabalize and move ever closer to the sun... So GTFO of dodge." Granted, a little bit more story is conveyed through mission briefings which are simple emails that you can read, but they can be generally skipped and are rather dull outside of the odd running joke. You make your own story in where you choose to go in the capaigns, and how you choose to handle each battle. Personally, I prefer this method, as games like Homeworld 2 get obnoxious with their incessant in-game cutscenes and endless hand-holding. I'd rather play my game, not watch it.
Overall, I'd say that Earth 2150 is the most innovative RTS out there, and certainly amongst my favorites along with Dawn of War, Homeworld, and the first StarCraft. It surpassed its predecessor "Earth 2140," and set a high bar that its sequel, "Earth 2160," sadly fell just short of. If you're a hardcore RTS player, I highly recommend this game.
I forgot to mention a couple things... The controls are quite unfamiliar. Being amongst the first 3D RTS games out there, they messed with the controls quite a bit. Being that this game lacks a tutorial, I strongly suggest downloading the manual, or finding a quick reference guide for the controls. Also, the prerendered cutscenes in this game are pretty damn awesome. Sadly, they are compressed to hell because they use the old bink codecs, but the quality really is top notch. Think about what CG looked like in 2000, then compare it to this... Really, the only places you'll find better is in studios like Blizzard.