The Binding of Isaac: Afterbirth Review (Jimby)
I was very excited for this upgrade when it came out, especially because it introduced mod tools.
Unfortunately, it introduced the awful portal mechanic and made the item pool much too big for consistent runs. My win ratios plummeted, the runs I enjoyed became much more rare. The game became much harder, and my progress on completion marks slowed to a crawl.
I still enjoy the game, but really enjoyed it more before I corrupted my experience with this upgrade.
More recent tweaks reigned in the difficulty of the portals, but many of the biggest issues with balance in this DLC weren't fixed in it, as they could have been, but require the next DLC which has even more item pool pollution issues.
In my mind the glory days of Binding of Isaac ended with Afterbirth 1, and I would recommend new players just stop there.