One of the oldest continuously inhabited sites on Earth, with layers of Neolithic, Bronze Age, Greek, Roman, and Byzantine settlement stacked on top of each other in the green Jordan Valley. Unlike Jerash's single dominant Roman-era layer, Pella's appeal is in seeing that full stack of civilizations side by side — a Roman odeon a short walk from Bronze Age tell mounds still being excavated.
Pella is about 90 minutes north of Amman (130 km) in the Jordan Valley, and roughly 30 minutes from Irbid — usually combined with Umm Qais on a full northern-Jordan day trip.
Spring is genuinely the best window — the Jordan Valley's lower elevation means it's noticeably hotter than Amman in summer, sometimes uncomfortably so for walking an exposed archaeological site.
Excavation is ongoing here, so parts of the site may be roped off or actively being worked on depending on when you visit — that's normal, not a sign you're missing something. Combine with Umm Qais since both are in the same general area and pair naturally into one northern loop.