I have two groups I and running through a scenario, I thought I would put my observations here. We've just started, I'll add more as we play.
The first group is 3 magi and a summoner.
Two of the magi chose slide casting, and the third chose shooting star with returning javelin, which I thought was clever. All three had plenty of fun with their schtick, and the shooting star player didn't seem annoyed about not getting the free move. There was plenty of talk at the table about how cool the various magus feats and features were, and they all made liberal use of the fact you can hold your spell in your weapon for a round to split a spellstrike up, which made them able to be more flexible with their actions than I was expecting.
The overall first impression from the magus players was that it is a class with lots of fun ideas, but missing most of your spells makes it a bit of a bummer in practice.
The summoner kept getting tripped up by manifesting taking a full turn. They were moving through a foggy town, not knowing if the next creatures they encounter are going to be monsters to fight or panicy townsfolk to rescue (who might freak out about her ghost), and guessing wrong meant she lost the first round of combat. Everyone felt a full round to manifest was punishing.
Once in combat, though, the eidolon proved a powerful tank, what with the summoner standing out of danger healing herself. The player seemed satisfied with it's attacks and damage, even though she only used boost eidolon once.
Some of them have been liberal with their slotted spells, so we'll get some data on their endurance in the next session, I'm sure.