I'd suggest playing an RTW v1.3 campaign on large unit size with M/M difficulty as Scipii. Remember to CTRL-S and CTRl-L before hitting end turn. Use minimal_ui, remove the green arrows and banners, turn off the radar map and keep the camera low for a nice battlefield experience. Auto-resolve battles against rebels to avoid the tedium of eliminating them, but play all the other battles.

STW and MTW/VI use a different battle engine than RTW. MTW/VI has some enhancements to the morale system, but it still works fine in STW. MTW/VI also has the smartest general in terms of not getting himself killed, and cav flanking is enhanced over STW. The STW/MTW engine has a stronger rock, paper, scissors system, and stronger terrain effects. The AI is smarter about using terrain in the STW/MTW than it is in RTW. Also, the units don't run as fast as they do in RTW, and they fight longer especially in STW where the rout point is lower. STW uses smaller maps, but this size is actually what the earlier battle engine is optimized for along with normal unit size. MTW went to larger maps, but the fatigue rate was not re-optimized for this larger size and tends to be a little too high. Strangely, eventhough the fatigue rate is lower in RTW and the maps are smaller than MTW, the AI units get exhausted if they have to cross the entire map which is apparently due to all the extra running around the AI does with it's units. The combat penalties due to exhaustion are fairly strong.

The reinforcement system in STW/MTW is problematic. You can get long streams of reinforcements entering the battle as depleted units leave. This wasn't too bad in STW because the maps were small and units always rout directly back to a single entry point, but on the larger MTW maps the reinforcements have a longer distance to travel and routing is away from the threat so battles can end up being very long. I've had many MTW battles that lasted over 1.5 hours and a couple that lasted 3 hours when lots of reinforcements were involved. I think my longest battle in STW was 1.5 hours. In RTW v1.3, the time spent fighting battles and spent doing things on the strategic map is more equal than in STW or MTW. Re-inforcements are handled differently. The longest battle I've had in RTW v1.3 is about 30 minutes.

STW is interesting because it has guns and no artillery. MTW, set in an earlier period, has very weak guns and artillery that doesn't move. The AI doesn't use artillery very well in MTW, and it brings artillery to field battles which isn't appropriate. You often see the AI when on defense move it's units to high ground in MTW leaving the artillery which can't move unprotected. When the AI is the attacker, all you have to do is keep your units back out of range. In RTW, the artillery can move and the AI makes good use of it.

STW has guns, but they are very strong in STW/MI v1.02 and they dominate any battle in which they are present. Some players like it that way, but they are definitely too strong for the battle system. It is possible to substitute STW v1.12 gun stats for those in STW/MI v1.02. Also, the battlefield ninja and kensai are questionable because they can't be adapted to the battle system very well. The system was not designed to model small but powerful units. For instance, I've spent many hours trying to balance the kensai in the Samurai Wars stat for STWmod for MTW/VI, and can't do it. In this sense, original STW v1.12 which didn't have battlefield ninja or kensai and had weaker guns gave better balanced battles. The weather system is a lot more varied and tactically important in STW than it is in MTW, and the seasonal turns impact the battles and require more planning in your ecomomics.

In general, as the number of unit types has increased in Total War games the playbalance in battles has deteriorated. This isn't so much of a detriment in SP because better units have higher support costs and you have to build up a tech tree to get those units, but it's a major issue in MP since there are no support costs and all units are available for purchase.