Summoning.

[Bloodred]

I too found obtaining the Eidolons to be quite difficult, Bahamut for example, I literally got one second before I would have died from doom. I only really used them if I was being lazy or I noticed I was about to stagger an enemy for burst damage, again Bahamut for example, to do a quick 400k damage. They were boring to use because all you had to do was tap x repeatably as there was no point pressing the buttons yourself. On a last note.. I couldn't even pronounce some of their names!

I prefer them in previous games where they come with a nice little scene, do their attack and disappear until summoned again.

[Fleur]

In FFXII, you have the option of cycling through party members in the battlefield, while FFXIII limits you to one controllable character in battle - your party leader in a sense. At least in FFXII by cycling through characters you can have each of them summon their Espers without changing the party lineup constantly, whereas in FFXIII I was mainly limited to Odin for the latter half of the game. If I wanted to use another Eidolon, I'd have to edit my party lineup (and perhaps all the Paradigms again) and therefore I found little point in doing that, especially as the Eidolons weren't exactly spectacular.

They're certainly more effective than their FFXII counterparts however. The Espers in that game either die easily, inflict very little damage or make it so difficult to pull off their finishing attacks depending on who the Esper is. At least with the Eidolons in this game they can have some use in fully healing the party once dismissed - as well as being capable of staggering an opponent at times, though that's basically it. With the battles concluded by a timer, I find that Eidolons slow you down more than anything when your party of three can inflict the same - or more damage in the time you use the Eidolon. Still, at least they don't die in battles like the Espers easily do. The Gestalt thing is pretty silly I have to acknowledge that. I'm really unsure why having transforming summons and treading on Gundam or Super Robot Taisen territory was even necessary anyway.

[Gingerbread Lesbian]

I found the summoning in Final Fantasy XIII almost useless. The only use I got out of summoning was if a character died they would be revived because of the summon and to knock the Adamantortoise down straight away. As far as actually battling with summons, I never did unless I was forced to when I used them - attacking with 3 characters > using summons.

[Lirael]

I can't remember summoming the Eidolons very often at all in XIII. I didn't really like how they were controlled in battle. The fact they ate up TP was also somewhat frustrating. However, I don't feel XIII was a worse game for this. Summons have always been a bonus in FF games for me rather than a necessity. X is the only game in which I viewed the Summons as characters; I grew quite attached to Yuna's aeons.

Unlike XII, which I feel gave the summons very little purpose at all, the use of Eidolons in the story of XIII was fantastic. They weren't important within battles, but they were integral to the concept of l'Cie and man's relationship with the loving goddess Etro. The Eidolons aided each character at key moments in the game, often providing them with a means to escape - even crash a party. Furthermore, the Eidolons were well matched to their characters.