Eh, the stock count won't change the poor matchups or the engine and meta of Brawl. It does speed things up, but at the end of the day, it is still Brawl. Nothing wrong with that, I just fail to see how 1 stock will accomplish much outside of speeding up events, and maybe alleviate stock-lead camping. /shrug, I do, however, find it much more entertaining than the normal format.
Some characters recieve notable consistency that they lack in the normal ruleset for brawl. Lucario doesn't receive a stock-differential aura boost, Olimar doesn't have to respawn and pluck a new pikmin herd, Squirtle, Ivysaur, and Charizard are actual choices and don't suffer stamina now, Zero Suit Samus keeps her armor pieces for the duration of the match, and Wario gets a more consistent number of wafts.
The other major difference is the value and mental aspect of the game. An old adage in smash goes "Play every stock like it's your last." That is, play as if every decision and every execution is the most crucial for you, or simply "play with 100% of your being." In three-stock Brawl this is how it is approached for the full time -- Players will wait, stand, walk, and generally make for a show about as interesting as a staring match for as long as they can to fatigue their opponent. It is a constant battle of attrition where there are no real winners, just a person who ended out with less fatigue.
With the one-stock matches, this mindset plays into games, rather than stocks, and makes the whole thing go by faster (A total of seven stocks over twenty-one minutes exist, rather than fifteen stocks over twenty four minutes). Instead of Ice Climbers getting a stock lead and stalling out while the opponent tries fervently to gain back a lead with 6:30 on the clock, the match ends at the same place the worthwhile effort does, on the first stock, and at 1:30.