I'd recommend giving it a try - and starting with the Normandy demo, since it's technically the most up-to-date and actually has a couple of "real" and fairly big scenarios. There are a solid 20+ hours you can spend playing the demo alone (if you take both "real" missions in it and play them through from both sides).
Combat Mission is great, although I'm obviously a little biased since I've been playing them for 12 years now. I'd also say that all things considered, the graphics are actually great rather than poor - because normally in this type of game, you're moving icons on a 2D map. It's a full-fledged tactical wargame at an extremely high level of realism, where you can command up to battallion-scale engagements in 3D with each and every soldier animated, with destructible objects and terrain, a sophisticated (if quirky and sometimes weird) tactical AI which makes soldiers a little more than just mindless drones that go exactly where you click and die with no questions asked. So there's not really any other one that does what CM does - the closest comparisons are Achtung Panzer/Graviteam Tactics (which certainly has similar tactical depth, but lacks breadth and is real time/single player only) and Close Combat (which, however, is purely 2D) series. Every other strategy game out there with a similar level of graphics is a toy by comparison.
There's a fair bit of homework (manual reading and learning) and a while that it takes to wrap your mind around how it really works and where the reward of playing something like Combat Mission is, but once it clicks you'll never want to go back
