I've seen all of these movies separately. One time, perhaps twice, I did watch all of them in succession. A Jaws marathon.
They all share a vibe. You know what I mean.
The first is great, the second is very good. The third is average at best. But it has potential. A lot of potential. The fourth film starts out quite good, but turns out to be below average. The potential is squandered in the 2nd and 3rd act. The 4th act is ridiculous. Part IV does have Michael Caine.
Worth the watch if they are all on together. Otherwise, the first and second. You don't need the second, unless you have a penchant for the Jaws vibe that I mentioned earlier. It's very late 70's, which had tremendous production value.