I agree that good encounter design (and, just as importantly, players who are willing to go along with that encounter kind) go a long way to reduce the boredom of combat, and it's a tool I've been using for a while. Varying primary goals (eg. hostages, timers, races, deathtraps) are the most suitable, because the primary goal in this case does not necessarily force combat.
I disagree on the "an encounter that you can mow through with nothing but standard attacks is an encounter with no element of risk to begin with". D&D encounters have been built around the dice game principle forever, and while there may be risk of dying, depending on the opposition, it's still a dull encounter (unless you find it exciting to see if you can roll a 20 when you need one, in which case straight up gambling might actually suit you better). The virtuoso fencer: getting the steel out of his hands sounds like a good idea, but should be almost as hard or harder than beating him down, if he really is a virtuoso fencer - lateral thinking would involve something altogether different in this case.
So agreed on the encounter design. However, what I wish for (and realize I'm not likely to get) is a system that encourages different actions, even in the "regular" beating down the bad guys. Or in other words, to me there are two ways of solving the combat issue in RPGs: make it short (ie finish a combat in sub 20 mins), which hardly any game does, or make the combat subgame an actual game that's worth playing (which also hardly any game does). D&D 4th tried the latter, but the result was, at least to me, not engaging enough to sink time into, and it took way too much time to finish combats.
FC is way better than most games in that you have advanced actions (which, for the record, I use extensively, even when they are less efficient, because it keeps me from getting bored in fights), but as pointed out, there still is a heavy slant towards the standard attack that makes it a favored option. Any optimal option (towards which I count the Feint/Attack with sneak attack dice combo) makes things less interesting.
Attack options that set up combos or open up actions that are otherwise not available make things more interesting. The mix-up trick is good. Actions that allow you to improve your chance to hit (like Feint) are good, but usually only if they can be followed up with actions that do more damage (which is how feint is used most commonly in practice). As long as you can compare action-to-action, optimal choices are easy. Once initial choices branch into additional choices whose efficiency increases as they are chained, optimization gets a bit harder, and things get more interesting.
Just think of board games: a game with a single obvious strategy will be won by the person with the most luck, which is unsatisfying, so you won't play the game often. If the game has many different paths to victory that vary significantly from the outset and may have to be rebalanced during the game, and the strategies are difficult to weigh against each other, then you get something that people come back to. While I think FC is taking steps in the right direction, it hasn't reached the latter, but I think it has the potential to do so with a few small tweaks, and those are what I'm looking for.
OK, done with off-topic.