One thing that I really like about Super Robot Wars: Original Generation 2 is the complexity of the individual battles. As I mentioned in some of my earlier posts, each battle in Original Generation 2 tends to have several twists and complexities. As a battle progresses the Mission Objectives constantly change, new enemies appear, you get reinforced with allies, and even very important story scenes will often occur in the middle of a fight. In some later missions of the game, the title for the current mission will not even appear until you have defeated dozens of foes and accomplished an intermediate objective. There are a few particular schemes to this complexity that all work very well to different ends.
One of the most basic situations in SRW:OG2 is a battle which begins with only a few units under your control until a large group of allied reinforcements arrive (usually along with one or both of the battleship/carrier units). In this situation, the starting group is always mandated by the plot, and the reinforcement group is usually chosen by the player from the full list of available units. Often, it is a losing condition for the first phase of the battle that you can't lose any units, but this changes to the normal loss condition (all units lost or loss of a battleship) when you are reinforced. This set up is incredibly predictable because of how often it is used, but at the same time I can understand why it is used so much because it works well. It allows both a significant part of a battle in which a limited number of characters get the spotlight (often combined with the challenge of facing a large number of enemies with only a few allies), and at the same time allows for a battle phase in which you can use whatever units you want (which is important for building up the strength of the units and getting a chance to use even minor characters in the cast). It allows both the opportunity for detailed story sequences and desperate situations with a few characters and full scale battles with an entire army, within the same mission. This structure is really good at helping develop different stories within such a large cast.
Another very common shift in battles is the sudden emergence of a boss unit instead of or along with a normal wave of enemies. In many cases, the emergence of a boss is unanticipated, and severely changes the tone of a mission. A mission which may have been a straight-forward battle against a large number of grunts can suddenly transform into a desperate battle for survival in which you have to somehow hold out long enough to escape (this is very common in early missions). This tends to be very dramatic, and serves a few important gameplay purposes. First, it provides a good chance for the player to build up money and experience, even in the "desperate survival" type of mission. Second, it lets the player build up the important "Will" stat before a boss battle, which can only be easily gained through defeating many weak enemies, but is very important for defeating a boss. Finally, it helps add to the distinct challenge of OG2 boss battles, which are simultaneously terrible wars of attrition (you need every last scrap of energy, ammo, and SP to win) and races against time (mot bosses regenerate health terrifyingly quickly, so if you let up at all our effort will go to waste and the battle becomes impossible). Having a large number of enemies before a boss fight means that you must fight those enemies far more efficiently than usual, which is a good challenge.
One final trend in battles is that new units almost always get a chance to show off. Either the new unit will start the battle on its own, or it will join your forces in the middle of a mid-battle story sequence and attack a major foe in a spectacular fashion. Either way, most units will have an entire mission centered around their introduction. This aspect is pretty clearly tied to the way SRW games are built around things being blown up in very flashy ways, and the whole effect is a lot of fun. Certainly, it is far more interesting than just dumping characters into the team without going to any effort to make them memorable.
I think it is a shame that more games in the tactical RPG genre don't have such complex battles. Of all of the tactical RPGs I have played, only the Fire Emblem games have anything resembling the kind of major mid-battle events or as many twists to a single battle that are seen in Super Robot Wars, but even in Fire Emblem battles tend to have little story and remain mostly static. Despite being one of the great defining games of the genre, Final Fantasy Tactics only has about two battles in which there is any kind of mid-battle event or change to the starting battle situation at all, and both are merely cases of an enemy already on the battlefield transforming into a monster rather than dying. In Final Fantasy Tactics, or almost any other game in the genre, enemies don't even get reinforced, and battle objectives are static. In such games, battles are treated as only a challenge to be overcome between story events, not as story events in of themselves, which means they don't ever reach their full potential.