AS has a lot of pluses, but it is not a Skyteam member and likely never will be one. Depending on your travel and redemption pattern and award-vs-benefits priority, it can be great or awful.

Pros:
1. It's promiscuous. You have both a number of Skyteam and oneworld partners, plus some non-alliance partners like Icelandair and Emirates.
2. EQM status miles on some major partners: Delta, LAN, and I think AF/KLM counts for EQM on AS even though AS doesn't count for them.
3. Upgrades on Delta.
4. Some elite benefits on Delta and American comparable to their elites.
5. Some reciprocity on paid lounge membership.
6. Awards options available on partners including an AS connection.

Cons:
1. It's not promiscuous enough. You are missing many Skyteam and oneworld partners.
2. Some big gaps with many non-EQM partners: no EQM on BA, QF, CX, KE for example.
3. You are behind the lowest Delta Silver Medallion for upgrades even if you are an AS MVP Gold 75K. That said, as a regular MVP Gold I once got a DL upgrade on a CR9 DEN-SLC so it's not impossible. Not that it was a great score!
4. Not full reciprocity on DL and AA elite benefits and no way to upgrade on AA.
5. No reciprocity on status-based lounge access. AS 75K isn't getting you into an Admiral's Club, Delta SkyClub, or any other oneworld or Skyteam lounge even on an international itinerary.
6. Awards can have only one partner plus AS (incl AlaskaHorizon regional) in the itinerary.

It's a viable option especially for USA-centered Delta flyers but not a full Skyteam (nor oneworld) replacement.