I get that the summoner is, well, a summoner, but I feel that the "summon monster I-IX (and then gate)" ability the class gets is pushing it a little far. The main goal of the class seems to be its uberpet with the actual summoning put into the background. Personally, I feel that encouraging the summoner to use summoning spells makes the class a nightmare to use within the battlefield--the summoner is one character, his eidolon is another, and his summons are another whole batch of characters for him to control.
That's a little much.
What I might suggest instead of this is allowing the summoner to get bonus conjuration spells from other spell lists to add to his spells known--perhaps in the following manner:
Level 3: Add one 1st level spell from wiz/sorc list to your 1st level spells known.
Level 5: Add one 2nd level spell from wiz/sorc list to your 1st level spells known.
Level 7: Add one 2nd or 3rd level spell from wiz/sorc list to your 2nd level spells known.
Level 11: Add one 4th or 5th level spell from wiz/sorc list to your 3rd level spells known.
Level 15: Add one 6th or 7th level spell from wiz/sorc list to your 4th level spells known.
Level 17: Add one 8th spell from wiz/sorc list to your 5th level spells.
Level 19: Add one 9th level spell from wiz/sorc list to your 6th level spells.
Thoughts?