Atletico deserve so much credit here. They will be the only team who goes to the bernebeu and stop Real from scoring this season, and that is after conceding only 1 goal against Barcelona in 2 legs in the Spanish super cup. They limited Real to scraps pretty much all game until Morata came on and caused a few problems, and it really should have been more comfortable with the chances Atleti wasted (Tiago and costa the main culprits here). Plenty of feigning injury and surrounding of the ref by both teams but if you watch Spanish football regularly it's nothing out of the ordinary. Atleti broke the hoodoo of over a decade without wins v the rival and now have 2 wins at the bernebeu in the space of a few months. Superb stuff.
I never used to rate Costa but he has developed into an absolute beast. Keeping up with Messi in the goal stakes and a problem for every defender. He's not on the pitch to make friends and part of his style is to play on the edge. Arguably Atleti are a better team now than the one with Falcao, who's departure isn't really missed at all. Hope they can keep up with Barca and stay ahead of Real this time around.
Diego Costa and Villa are both more complete forwards than Falcao IMO, which would explain why the team as a whole is performing more fluidly. The only downside would be that they at one point might miss what Falcao offers, i.e. clinical finishing. As outstanding as he's been (and to me he's been the best performer in La Liga so far, slightly ahead of Cani, Koke and Valdés), I don't think Diego Costa can keep this kind of goalscoring form (basically 1 in 1) up for an entire season. Villa and Leo Baptistão aren't 20-goal/season strikers either at the moment. They have some options from midfield, Raúl García and maybe Arda, who could chip in with some goals, but at times I do think they'll struggle to score. They should still play better than they did with Falcao in the line-up; his best performances always seemed to come in the Europa League and the European Super Cup, and far more intermittently in La Liga.
Defensively they're still the best side in Spain (31 goals conceded in 38 games last season, earning Courtois the Zamora after all the Valdés domination; 5 in 7 so far).
Last season their record read: 3rd place with 76pts (9 behind RM, 10 ahead of Real Sociedad), 23W 7D 8L, 65-31 (+34), and they sat in 2nd for 24 weeks (!!). Their top scorer was Falcao with 28 goals (Diego Costa scored 10, he's currently already on 8). Their top assister, Koke with 9 assists (currently on 6). I do believe they can cut out some of those losses from last season (they've already turned one L into a W, away to RM), and even if they don't win those they're more likely to draw than lose IMO.
Others...
Sevilla have been really underwhelming I've got to say, Valencia doing better than I though they would actually, Real Sociedad struggling to find that awesome consistency from the 2nd half of last season again (what was it? only losing 2 games after the 10th Jornada, 2 losses in their last 28 games that season; Montannier seemed to get a lot of stick from Real Sociedad fans but he did get them playing outstanding football AND get incredible results at the same time).
Málaga actually don't look all that weakened, defensively they're equally (and possibly even more) sound than last season (in which they were headed for best defense until their late collapse following the Borussia Dortmund debacle), Schuster has been quietly excellent. Rayo are a prime candidate for relegation IMO, already 21 goals conceded in 7 games but even more concerning for them, only 5 goals scored. The overhaul has been too big and now they can't match the amount they concede with goals of their own anymore. Espanyol and Athletic are also looking stable and might challenge for European places, Betis have regressed a bit in that aspect but still might make it. Almería another one that I've been impressed with, although they're still to pick up a win they've been playing very good offensive football and aren't looking like the sieve they were last time out in La Liga.
Even considering what Atlético are doing, I'd still put Villarreal as the surprise of the season so far. Just how they ended up relegated two seasons ago is still a mystery to me, but they've started off brilliantly now. They remain unbeaten after 6 games (tonight big away game to Betis) and should've demolished RM. Cani is in the form of his life and the balance between offense and defense is looking good. The only concern would be that their squad is pretty thin, so far that reason I'm not sure whether they'll be challenging for the European spots.
Also, another quick thought on Diego Costa; that loan-spell at Rayo two seasons ago did him the world of good IMO... really people if you want to change a player into a goal machine just send them on loan to Rayo... Michu, Piti, Diego Costa, maybe this season Alberto Bueno, if they can get their act together that is!
My apologies for the rambling train of thought.