I'm fairly happy with Sanchez's signing, though I presume as with Ozil, it likely means ignoring the biggest changes that needed to be made.
A new actually good left back would improve the team more than say Podolski > Sanchez. I'm also guessing Sanchez starting will at best just make Pod or Caz very unhappy with lack of games, or at worst, one of them leaving before the end of the transfer window.
How Sanchez will do... I don't know. He often went fairly long spells without scoring or assisting for Barca. He score a couple key goals, but the games he effected the most weren't the big games. Barca were on the downslide when he joined though and had trouble with the bigger games.
Will he adapt well to starting every game, in a physical league, I don't know. He dived an awful lot at Barca, will he grow out of that(many players do), will he get loads of yellow cards for it, or win loads of penalties from it, I don't know.
I don't know where he's going to play either, with Walcott fit I presume Wenger sees him as wide left(he's better wide right though). I'm not convinced he offers a lot defensively which with Gibbs behind him is potential problem.
Have to see how it turns out basically. If he can cut out the diving I think he has the potential to do very very well for us.
We just needed a left and right fullback more than anything, and a top notch central striker after that.
Chelsea had a problem with strikers, so they bought a striker, they didn't have a good enough DM so they bought a DM, they need a fullback so are buying a fullback, and they got Fabregas because you don't turn down the chance to sign his quality unless you're stupid.
top teams fix the problems as a priority and bring in improvements after that if they can in general. We signed Ozil and ignored all the serious problems in the team. I fear that we'll sign Sanchez, while ignoring most of the problems.
I think the team as of a few days ago with two genuinely top fullbacks costing 20mil a piece would be a better team and do better in all competitions than adding Sanchez and Debuchy.