Denorfia is a right-handed outfielder, 34, who was perennially underrated before this season in which he's struggled mightily with the bat. In 2013, Denorfia was worth 3.9 fWAR thanks to his excellent defense in the corners and solid offense, but he's struggled mightily this year, only managing 0.6 fWAR. He's hit for a 76 wRC+, 85 wRC+ against lefties -- still well below his career levels. He's only making $2.2 million this year, so the Mariners will be on the hook for under a million dollars.
Given the state of the Mariners outfield, Denorfia will be an instant upgrade over Endy Chavez, and perhaps even the rapidly sinking James Jones. He should start against all lefties while playing all three outfield positions. Though his time in center field has been scattered over the years, Denorfia has grades out at least decently at the position, certainly better than what the M's currently have on the roster.
It's a small move, but one that does upgrade the roster. This won't be a popular purchase among many fans given the Mariners other needs, but simply by being a competent outfielder who has hit lefties well historically, Denorfia will make the Mariners better. Don't expect him to bounce back to his previous offensive levels, but if he does, it'll be a welcome surprise. If things stay exactly the same, Denorfia may provide the Mariners with an extra win of value or so over the rest of the year. Stefen Romero has been worth -1.0 WAR. James Jones is at -0.7. Endy Chavez is at -0.2. Even acquiring a replacement level outfielder would help the M's at this point, and Denorfia is currently better than that, with the chance to be more. If you're not a believe in Abe Almonte, there's little to dislike.
This isn't a move that puts the Mariners over the top, and it did cost them Abraham Almonte, plus somebody else minor that we don't know yet. While Almonte looked miserably overmatched at the MLB level this year, he did show promise last season, although that hasn't carried over to this year in Tacoma, where he's been quite a bit worse than the year before. Given what the Mariners have for internal outfield depth, it's a little strange to be giving away any of their talent with any upside at all, so the price is questionable at best. There's still a chance that Almonte figures it all out and becomes a solid 4th outfielder some day, but those contact issues were pretty horrendous. It's a bigger gamble than the M's probably needed to make, but apparently they saw enough to give up on Almonte.
The other piece is Stephen Kolscheen, a reliever in Tacoma who the Mariners saw a bit of in spring training. He's been fantastic, striking out 33 batters in 32 innings while only walking 4 in Jackson before being promoted to Tacoma, where he's been equally great, sporting a 22/6 K/BB ratio. Kolscheen doesn't throw exceptionally hard in the low 90s, but the control artist thing while whiffing a batter per inning is still appealing. The Mariners have a ton of good relievers, so this is dealing from their surplus, but Kolscheen isn't a loss without potential impact, even though it's probably quite low.
Try not to focus on the sequencing of the moves today too much. Remember that the Mariners signed Willie Bloomquist and people freaked out, and then they gave Robinson Cano $240 million dollars and we all kind of forgot about it. If this is it, there will be plenty of criticism, since they're clearly being buyers and not sellers. Of course Chris Denorfia is not enough, but he helps.
For now, the main criticism should be on the Mariners for putting themselves in a situation where they have to trade for a slumping Chris Denorfia, not trying to patch together the mess that's currently in front of them. Whether this is a win or not will depend on Abraham Almonte's future pitch recognition skills.