Age of Wonders 3 actually bought be BACK to FE:LH.
There are just too many things missing from AoW3 that I enjoyed in FE:LH, such as the whole empire building component.
For me, the perfect game is FE:LH strategy component using the tactical battles from AoW3.
Things I like better in FE:LH:
1. There is just more to do. I found the first few hours of AoW3 *awesome*, but then it gets boring very quickly.
2. Heroes feel more powerful, and hero levelling up feels more meaningful.
3. Hero gear is better.
4. Diplomacy is way better.
5. I much prefer the tech tree over the random spell research.
6. INITIATIVE IN COMBAT. This is such a superior system to AoW3 and allows for such things like more than one spell in combat.
7. Much more powerful and interesting wandering monsters.
8. Improved quests.
9. The spells are more fun IMO.
10. Ability to build your own units, and much more in depth leader customisations.
11. The game scales with time better.
Things I like better in AoW3:
1. The tactical map graphics.
2. The tactical map combat system, very polished, reminds me of X-COM almost!
3. Optimisation seems better. FE:LH chugs on my computer on the strategic map.
4. The underground is an awesome concept.
5. Flying Mounts.
6. Sieges.
7. Unit stats improvements on level up.
I think AoW3 makes a great tactical war game, but I want much more than that out of a game these days, and I don't think it's asking too much to demand more. Unless they expand the strategic side significantly, I don't think I will be going back to the game, which is a shame, because what they have achieved in the tactical side of the game is pure awesomeness.