Houston Astros are still defending their title from last season. They have a rock solid team, probably best in the AL all around IMO entering the Postseason, even better than the Rays and Orioles.
Texas Rangers were in first place for most of the season. They struggled at the end of August and beginning of September but came back strong over the last 2-3 weeks of the season. They have a really exciting lineup. Rotation isn't anything elite, but it's solid. If they get Mad Max back, even better! Bullpen has looked shaky at times but they have some high K guys back there. If they made the World Series, I wouldn't say it was pure randomness or a fluke. They had a really good team during the regular season, played a different Rays squad than from May/June and then played a young and inexperienced Orioles team with a long layoff and weak starting pitching.
Phillies also were a strong WC team. They went to the WS last year, knocked out the Braves again two years in a row. They have some star power in Harper and Turner (who has been hitting better) along with some other solid contributors offensively. Rotation wise, they have Wheeler and Nola, along with a really good BP.
D'Backs are pretty much the only team that has sneaked through this far that wasn't expected to. They did play the Brewers and Dodgers at the right time in a short series. I'm not sure how they do in a 7 game series however against the Phillies or how they would do in a 7 game series against the Astros/Rangers. They are the weakest team remaining obviously.
Otherwise, I think both the Astros and Rangers deserve being in the World Series, and Philly as well. So 3 of the 4 remaining teams.