I really miss having an army of robots, rather than skeletons and zombies, or wolves and bears.
I definitely haven't found a game to scratch that Mastermind itch, but I keep trying. Some games I've tried:
If you're okay with a Diablo-alike, Marvel Heroes has a bunch of characters with various types of pets (Magik, Dr. Doom, Ultron, Iceman, Loki, Rocket Raccoon, Luke Cage, the Thing, Squirrel Girl, Emma Frost, Vision, Rogue with the right stolen powers, and so on) as well as many pieces of gear that have a chance to proc summons on hit or on being hit, as well as Sidekicks for all characters (which can be set as permanent companions, temporary summons with increased stats, or as temporary summons with normal stats that provide passive powers when they're not summoned). There's no way to directly command any of them, though.
Star Trek Online almost always gives you an Away Team for ground missions, giving you a group of minions with diverse abilities. If you take the Engineering path, you can also summon attack and defense drones and turrets. (If anyone on your Away Team is an Engineer, they can also summon drones and turrets of their own)
Lord of the Rings Online (which I just started playing yesterday) has two pet-based classes: the Lore-Master (a Controller/Dominator combo that summons animals) and the Captain (a Tanker/Defender combo that summons human fighters). They can each only have one pet active at a time, but both classes have a full pet command bar with many of the same options as CoH (Attack/Follow/Stay commands, Aggressive/Defensive/Passive stances, plus a "join me whenever I attack something" toggle in addition to the others), but you have to activate their special attacks (also on the pet bar) manually. The pet itself will only use basic attacks on its own. My biggest issue is that, like many fantasy MMOs, the characters run at a snail's pace (in order to encourage you to buy mounts later for long-distance travel).
Dungeons and Dragons Online doesn't have a specific summoner class, but most spell-casting classes (Bard, Cleric, Favored Soul, Sorcerer, Warlock, and Wizard) have access to the Summon Monster line of spells (Summon Monster I through Summon Monster IX), Druids and Rangers get the Summon Nature's Ally (I through IV) line of spells instead, and Artificers can summon Flame Turrets. Any class can also hire Henchmen and Hirelings.
I should mention Dofus, because I've been playing it even longer than CoH. There's two primary summoner classes (Osamodas, which summons animals and monsters; and Sadida, which summons voodoo dolls and trees), but twelve out of eighteen classes have at least one summon spell (and even the six classes that don't normally learn summons through leveling can learn optional summon spells). Only certain summons are controllable, and only in certain specific situations. The combat system is turn-based and grid-based (like Final Fantasy Tactics or the old Genesis Shining Force games), which may or may not appeal to you, and the game gets very hard at higher levels (with most monsters easily tearing through your summons, often in a single hit).
So while none of them are really like the Mastermind, there's some ideas for games with summon-based classes.