Just yesterday we played a game using the indoor side of the LOSH starter set map. I've got a question regarding the use of the transmatter gates.

The map states that "when any character occupies a transmatter gate at the end of a move or power action, it may be moved to any other unoccupied transmatter gate on the map."

A fellow player said that to use that transmatter gate is similar to using a teleport pad and requires a power action to activate. Is that correct?

For instance. I moved ganthet to a transmatter gate, that was the move action, after i moved him to the orange-lined square i moved him to another gate with thanos a few squares away from the gate. Was that move with ganthet using the gate legal or should i have first given a power action, as the other player said? I've read the rules on the map and i believe what i did was legal. Could someone clarify this please?

I think your interpretation was correct. Compare the wording to the wording on Teleport Pad:
The LoSH map does not mentiuon anything about having to give an action - it just gives a statement on when you may use the gates to transport yourself.

Interesting, since it also says at the end of a power action (added for HSS and such) You could run to the gate and teleport for your first turn, and on the second push to use RCE or CCE on a target near it and then teleport away when the action was complete.

Thanks for the quick response guys. Come to think of it that gives this gate map ability some interesting uses. Again Thanks

To take this further the text doesen't even specify that the teleporting character has to do the power action. You can TK someone onto the gate, teleport them, RCE/CCE, teleport back.

It doesn't, but the RA has ruled that it doesn't work that way.