It would appear to be a ton better. As others have stated, it is now able to properly replenish the losses of its armies, which makes it far harder to steamroll the AI. Even against city states, it can be somewhat difficult. One user posted on Massalia. I was defeated in a battle against Massalia first time I used this mod, though I managed to recruit more troops and return to the fight, defeating them in 2 more turns.
Against Veneti, I really had some interesting problems. They marched one of their stacks against Massalia (which I had just conquered) while I used the fact that their armies were away to take their city. I thought the campaign would be done there... I was wrong. The army around Massalia lingered and I was forced to destroy it. More importantly, the Veneti returned a fleet from Greece which I did not know they had and immediately attacked one of my cities in Italy (I forget the name; the one below Veneti on the east coast). It was some time until I could retake it.
The more spectacular changes are in the battles themselves.
It depends what the odds are, what faction you are, and how well you can maneuver. I've had battles where I've crushed 2,000 with 30 men lost. I've had battles where I killed 6,000 men and lost 5,000, and was defeated. It's all about morale. You can lose just 10% of your army and yet lose the battle if you really screw up.
The largest change is that almost no killing is done in melee until units route. There's the occasional guy who gets stabbed, but you can expect a unit of early (spearmen) hastati against huge numbers of ligurian heavy/medium spearmen to fight for 40 minutes with only half losses- if it holds the line and is not being flanked. In vanilla, the hastati would have been wiped out in about 3-4 minutes.
Instead, the battles now depend on morale. If outnumbered and flanked, units will break very quickly. This makes the battles feel authentic and I believe that a proper battle with FLAM represents a realistic ancient battle. In vanilla, even DEI vanilla, I never kept reserves. My hastati would just never flee, and they could hold for a while before taking grave losses, meaning that it was better to just make a long line to envelop the enemy. The pre-Marian formations therefore never made sense. It was better to spread your lines thin that to have reserves.
In FLAM, you really have to learn the meaning of reserves. If a line of hastati route, you must immediately plug the gap they leave. Otherwise, the enemy will start to break through your formation, curl around your other units, and they will roll through your army, causing it all to route. I learned this the hard way against Massila, and that still took 43 minutes. Units are now far more likely to regroup after fleeing, but make sure you have some "confident" units ready to assist a wavering line right away. I've started deploying my units in the pre-Marian style and it really is what you need to do in this mod. That way, when Hastati break and route, the principes are there to fill the gaps. If they route, then the triarii step in while you reform the hastati and principes who had routed.
Skirmishers and ranged units now have an actual use. In vanilla DEI I would just not recruit any. In FLAM, melee does little damage. Ranged, however, still inflicts damage very, very, quickly in comparison. This means that if you are able to take skirmishers into a position from which they can target the enemy (especially in their backs) skirmishers become real killers.
This is how ancient battles would have been fought. It was all about bringing in the right reserves at the right time against a weakness in the enemy line, or to protect your own. Now, lines can actually be broken and exploited and the game is no longer just about wheeling around the enemy flanks.
Thank you for the great mod! I love it!
PS: For the next version, I think you could reduce the stamina for the units. I've had units who have been constantly running or fighting for nearly an hour and are still fresh. I'd like it if units could actually get tired after 20 minutes of combat, but recover within 15-20. Ancient battles were also about bringing in fresh reserves to replace the exhausted ones, not just to replace units with low morale. In the real world, battle would not have been continuous. It was more often minutes of intense fighting between hours of bloodless maneuvers until one side gained the advantage. During the intense fighting, units would still get exhausted. While the bloodless maneuvering is not possible or even wanted in a TW game (imagine a battle which takes a day!), I think that fatigue should still be in the game. My hastati are currently Olympic athletes on steroids.