I've seen a gameplay video of it (I don't think it was Ricky Royal's, although I have seen some of his other vids); I like how it's a board game that kinda folds in some deckbuilding-game elements, but one thing that always frustrates me about the deckbuilders I've played (mostly Marvel Legendary and the TOS deckbuilder) is that it seems like once you really get powered up, the game is pretty much over (because you can accomplish the victory so fast once you get to that stage of development). Does Frontiers have a good, meaty length that doesn't end shortly after you get your crew where you want it to be?
I'm not familiar with Marvel Legendary, but I do play two of the Legendary Encounters games, which are quite punishing. Frontiers stays one step ahead of the players. Yes, you can build up abilities, either through cards, tokens, or crew. However, those opportunities can run out fast. The final tiles, where the Borg cubes live, have few easy opportunities for conquest, and fewer for repair. If your deck isn't strong enough to defeat the cubes, you may have to backtrack to a planet or base, perhaps discarding cards for lesser movement abilities. You can also gain abilities by leveling up, but each level becomes increasingly more difficult to reach. Crew are a big help because they don't go into your hand. However, they can only be used for one ability each turn, and you can only have as many crew as your current level allows.
It is never simple to defeat the Borg cubes, but if you do find it's too easy, their power can be literally dialed up so that they are more difficult. The damage you take can clog of your deck fast. Combat is deterministic, meaning you aren't going to just blow up (unless you play deliberately poorly). If you lose, it will be because you ran out of resources and time. Winning, on the other hand, feels like an intellectual accomplishment.
The game has a narrative curve where you have a lot of quick gains but in which successive accomplishments become more difficult. There are a limited number of enemy ships and bases to subdue: doing so gives you experience and special abilities cards. However, opportunities to defeat them run out. Away missions also provide opportunities, but you never know what the challenge will be until you commit crew to them (and it sucks if they all come back injured). Planets on Borg tiles are more difficult to encounter. Defeating the last cube often takes lots of planning, considering the cards you have left and what abilities you haven't already expended.
That does kinda concern me, because I'm the type of person who realizes halfway through a game that there was some major rule I'd completely forgot about. It's worse when you're playing solitaire (which I would be) because there aren't any other people to point out an omission.
The game is robust enough that some rules mistakes won't ruin the experience. The videos on Youtube should give you a sense of whether you will find it too difficult. Indeed, most people learn first from the videos THEN read the rulebook. And you should expect to have the rulebook always at your side.Learning the rules is doable, and this is by far not the worst rulebook. However, it has discouraged many from teaching the games to others--that's why it's often rated more as a solitaire game. There are actually two rulebooks. The first is a quick start guide which is fairly good. The problem is that the actual rulebook doesn't do enough to fill out the explanations from the quick start. The file section on BGG has a number of helpful fan-made supplements that can ease the experience.
Hope this helps.
