It's an interesting comparison. FE doesn't have the depth or balance of Dom3 (yet...?), but it does provide that good 4x fantasy feel. The factions are becoming differentiated in a good way, hero leveling is coming into it's own. The magic system is not as diverse as Dom3, and the tactical battles are not quite there yet (but I always hated the lack of control in Dom3 battles), but it's mostly a balance issue. Legendary Heroes is a stand-alone expansion. They're also currently offering LH for FE owners at half price, $20. Depending on what price you can get Fallen Enchantress for, it might be worth it just to purchase LH... it does include a lot of enhancements that polish the gameplay.
FWIW, there's quite a few Dom3 fans here on these forums, so I'd take that as a sign that if you like Dom3, you'll like FE/LH.
