Interesting use of terrain is always awesome to see...like Boxer's 3 rax block on Shakuras. I meant more generally, though...like what opener they decide to use and such. I thought MVP's TvP on XNC was very interesting vs Tester I think. He went for blueflame Hellion/drop (failed) and followed up with hellion/marauder/raven/banshee 1 base "all in" against an expanding Protoss. It's just fascinating to see what styles pros decide to use when winning "matters" with money on the line.
I remember watching some of the pro players and watching Terran use elevators for the first time. It blew my mind to know how to abuse certain things that each race has.
It's a lot different when viewing ladder replays and whatnot because people do a lot of questionable things on there for practice/fun. There's a lot of connectivity when pros are in the same situations that I'm in. I recall times when I've been in those cases and how I'd react and see what they do...great fun! In GSTL when the protoss player made Nexus first, I was just like okay cool, but no one would do that on a standard ladder map, so the rest of the game is just mostly going to be a foreign experience.
On ladder, you're allowed to play with a single build in each and/or all of your matchups if you want as it's very likely you're not going to run into the same players two or three times in a row.
Some of the benefits of the ladder is that element of cheese, which gives you practice against it in a situation where you're pressured to perform well. But outside of tournaments or having excellent practice partners, there's no other way to really practice being in a pressure situation than to play on the ladder.
That's not the case in a Best of X series, where you need to vary your play from game to game.
While playing ladder may not be the ideal situation for most players (see EGIdrA), most people will play their best and play standard. I find that a lot of the creative/irregular type of plays come in custom games where there's absolutely no pressure to play well.
EDIT: 15 Nexus is actually a pretty good opening at the higher levels against Zerg on larger maps. The Nexus first allows the Protoss player to pull ahead in economy as Zerg needs to be one base ahead to stay even. However, it's much easier to go with a 3 gate sentry expand as it's much safer than Nexus/Forge opening.
Just a random tangent -- my friend says he can beat most players on the ladder but not me because they are nowhere near as aggressive. I thought about this and figured out that those players probably are afraid of losing when they play. They won't attack if they think something might fail.
Same thing can be said about professional poker players. You have to be selectively aggressive, but always pushing and pressuring your opponents. EGiNcontrol calls the Starcraft equivalent of this as "shark mode." You want to be poking around at all time, controlling the towers, feign pressure or a push against your opponent, etc.
At the lower levels, indecisiveness and being passive is a downfall of a lot of less experienced and/or lesser-skilled players. They're too concerned about whether or not something is going to work instead of being confident in their own skills. This is where the skill gap that Azuremen brought up about units and balance takes effect.
If you're confident in your playing ability and utilize the shark mode mentality, you put your opponent on his or her heels. By forcing them to play passively and react to your aggression you can force mistakes and/or alter your opponent's plans.
When I play, I just want to learn/improve, so I just attack repeatedly until I'm convinced that something won't work. This way (making up numbers) I might be attacking 25% at bad times, but they are missing 50% of their attack opportunities. At the same time, I'm getting feedback of when it's good to attack, and they are just staying clueless.
Selective aggression and utilize the shark mode mentality. Learning timings comes with playing a lot of games which also develops your game sense. We all want to improve yet have fun at the same time!
I find this discussion is not only interesting but helpful! Let's keep it up!