When LoL in its current state is played between teams with 5 players of extremely close skill levels (as was the case for most of MSI), games are close, relatively exciting, and balanced on a knife's edge.
Below the pro level however, as seen in the recent College Championship, even slight discrepancies in skill levels lead to extremely unbalanced games. A total of 11 best-of series were played between the 8 qualifying teams. Of those 11 series, only a single one was not a sweep by one team or the other (aka 10 best of series were 2-0 sweeps or 3-0 sweeps).
These games were NOT exciting to watch, not compelling, and I would imagine, a total downer to actually play in. 2k Gold leads by 10 minutes is basically GG, and you can hear the announcers repeat over and over "even the smallest of mistakes/misplays cascades over the course of the game into gigantic advantages for the other team".
Take this down to solo queue where skill-level disparity between teams is often quite massive, and its easy to see why so many "games" are an absolute joke, with queue time/select often taking longer than it takes to decide the winner of the game itself.
I'm sure everyone has their own examples, but as a G3 player, getting paired with a Silver 3 support against a Plat 5 adc and Gold 4 support is going to result in a win 1 game out of every 100. Despite playing relatively well, the small advantages that their bot lane were able to accrue over the first 12 minutes of the game (read: kills on my noob support) shortly lead to a completely unwinnable game state as our top lane yasuo (who received all of our jungler's pressure) continued to feed and lose towers.
The point is, the game is clearly balanced around Pro Play, and is *fairly* entertaining to watch at that level (I say fairly since too many games devolve into Team A gets lead, proceeds to 1/3/1 enemy team to death without ever taking a 5v5 the entire game). However, at levels below the pro level, where there are clear differences in skill among the 10 players participating in the game, LoL is an absolute fiesta with most games being decided by 12 minutes, and the 30 minute average game time is just the time it takes for the winning team to slowly press their advantage and take your Nexus.