Now that the "ohh-ahh" factor has worn off with RTW, I've been playing a succession game of MTW along with a few friends alongside my new RTW campaign.
This is an extremely frustrating experiance. To put it bluntly, MTW makes me want to play RTW, and RTW makes me want to play MTW.
Things I noticed about MTW after going back:
1. The controls suck and its very "cumbersome" trying to move around when you're used to using the arrow keys in RTW. Also the whole left click thing is a pain in the ass, since you could accidently move troops when you're trying to select them. I do like the removal of the pink arrows when moving troops around and the fact you can keep them in formation/facing. Also - NO BUGS!
2. The UI is superior in almost every way to RTW's UI. The unit cards are much easier to see (1280x1024) display much more useful information. The game feels like you've got more cooler options to play with than the RTW UI, which takes up way too much space. Overall (when you get used to the MTW controls again!) its way easier to control your MTW army.
3. RTW battles have way more atmosphere. Graphics obviously, but mainly the sounds. MTW sounds suck compared to RTW. Can't hear arrows whizzing through the air, all your soldiers are silent, marching doesnt sound as cool, etc.
4. Strategy map. The MTW strategy map is very annoying now after RTW and its really hard to tell what the hell you're doing. You cant just glance over all your provinces and see if you're constructing stuff there. However the MTW strategy map has a very cool board game feel to it now.
5. AI. Overall the MTW AI on the battles is PROBABLY better than the RTW AI. On defence the AI in MTW manouvers way more than you see it do in RTW. Strategy map im not so sure, but the MTW strategy map is more simple than the RTW system so the AI doesnt screw up as much. Also the bigger MTW battles (combined stacks) is way more fun.
6. I used to have fun sieging in MTW but not anymore.
7. Movement speeds. In general movement speeds seem better in MTW. Apart from the fact that your guys slide around everywhere (which is point 3, atmosphere) they make more sense.
However its not perfect, cavalry seems too slow charging in MTW but too slow trotting around in RTW.
Also cavalry seems a huge anticlimax now in MTW (altho I dont miss the school of fish effect)
I charged some 66 Knights into some poor 15 odd tired miltia expecting them to be bowled over. But no. My knights just get "stuck" on them killing a couple then hacking away at them for ages before the militia routs. Which brings me to my next point.
8. I really missed the flashing flags for routing units.
9. Bugs. MTW battles go far smoother (especially sieges) without any bugs that want to make you rip your hair out.
10. Voices. This is partly point 3, but the guy for the MTW voices is so much better than the crappy Roman voice actor. He actually sounds his part. Troop voices are way better in MTW too.
11. Killing speed. Melee is vastly slower than RTW but at the same time it looks really stupid now. Large numbers vs Large numbers is way better and units take longer to rout. Large numbers vs small numbers however in MTW is incredably unrealistic and MTW seemingly lacks the snowball effect.
Everyone is complaining that the arrows kill too much in RTW but MTW is the same if not worse (it should be though, more powerful bows etc). I had 20 foot knights standing around being hit by arrow fire. I was concentrating on something else for no more than 20 seconds, come back, and I now have 3 foot knights standing around being hit by arrow fire.
12. There is more depth to MTW tactically. Formations in particular. Different units need different formations for different situations. RTW it doesnt seem to matter what formation you put your units in.
Really, both games feel like they've been made by different companies. MTW feels nothing like RTW. MTW (including the battles) feels like a grand game of chess, more of a strategy game like the oldschool hex based war games. I dont know what RTW feels like, part RTS, part civ game.
The big part MTW is lacking is in the atmosphere department and some clunky controls, but I have to say that if you kept MTW exactly the same, but gave it RTW graphics and sounds - MTW would be the better game.
The frustrating part is RTW could have been this, but it wasnt.
[Edit]I forgot to add, the AI in MTW has way more good generals. You might see one or two good generals in RTW but the AI has literally tons of them in MTW. MTW far far superior here[/Edit]