And, frankly, I would find it repetative and boring after a while - I mean, I could have fun with it for a few sessions, but after a while, it would feel like I'm always doing the same thing again and again with little versatility. So if I were asked the OP's question of what the slayer fighter loses in trade off? I would answer "fun that is brought in through variety" BUT, that's just me and a personal flavor bias thing.
You know in reading this I realized my Dwarf fighter is actually pretty repetitive as well.
This is his attack power list:
Fighter at-will 1: Reaping Strike
Fighter at-will 1: Wicked Strike
Fighter encounter 1: Steel Serpent Strike
Fighter daily 1: Driving Attack
Fighter encounter 3: Bull Charge
Fighter daily 5: Brutal Advance
His combats tend to go, Bull Charge, Steel Serpent Strike, Reaping Strike, repeat Reaping Strike until all enemies are dead. 2 of 3 fights he does a daily power (he is played in LFR). Wicked Strike is just there in case he gets an OA or something, maybe one day they will produce a Fighter at-will that isn't gimped that works in place of an MBA (unlikely now).
That really isn't that different from the Slayer in many regards, in fact a Slayer might change attack mode more often. What makes my Fighter more interesting than the Slayer is that as he levels he gets more things to do in a fight other than just damage (and he does ok damage already).
I did try re-building him as a Slayer, and it works, he does more damage, but he looses a lot of flavor in the process.
That said the "go to" race for Slayers seems to be the Half-Orc.
18 Str 18 Dex starting for +8 damage. Racial power that is functionally an extra use of Power Strike for free.
EG Level 2 Half-Orc Slayer
Str 18 Con 12 Dex 18 Int 10 Wis 10 Cha 10
Feats: WE: Axes (gives a re-roll for 1's on damage afaik), Power Attack
Stances: Poised Assault, Berserker's Charge
Enc: Power Strike, Furious Assault
Utility: Who's Next
Magic Items: Braces of Mighty Striking, +1 Vicious Greataxe (if your DM doesn't give you one you will save up and buy it)
MBA: +10 vs AC Hit: 1d12+11
Berserker's Charge: +13 vs AC for 1d12+11 (PA: +11 for 1d12+14)
Poised Assault: +11 vs AC for 1d12+11 (PA: +9 for 1d12+14)
Who's Next lets you get up to +5 more damage.
Base Crit: 23+2d12 (PA 26+2d12)
Power Strike or Furious Assault Crit: 35+2d12 (PA 38+2d12)
Power Strike & Furious Assault Crit: 47+2d12 (PA 50+2d12)
Other magic items: Badge of the Berserker, Horned Helm, Boots of Adept Charging (if you have a defender to lock things done)
Just wait for that "first round crit" from the Half-Orc slayers...