Download was about 3.5 Gb. From what I gathered it's an open beta like planetside 2 was (people are encouraged to spend money and there won't be a character wipe at launch), which seems to happen more and more with F2P games. It doesn't seem like any content is inaccessible for F2P players, what the cash shop seems to offer is mainly convenience items (character slots, bags, dyes, ...) and they're not nagging you about it either.
Gameplay is more action/twitch based like Cryptic's other MMO's (City of Heroes/Villains & Champions Online at least, haven't tried Star Trek Online).