In terms of major events that could be big enough to make up most of a season arc or a climax to work towards, we have, in no particular order as they might shift things around:
- The forging of the Rings and Sauron's intrigues with them
- The establishment of Mordor and the wars against the Elves / local Men that will likely go with it
- Internal Numenor struggles that end with Ar-Pharazon in charge
- Numenorean settlement of the mainland and establishment of Arnor and Gondor
- Ar-Pharazon's increasing hubris ending with the disastrous expedition against Valinor
- War of the Last Alliance
- More elaborate original plotlines they come up with, like the Harfoot stuff, or perhaps something set in the East or South

Compressing all that together within a decade or two, or even within a handful of years, is awkward if you start thinking about it deeper - for instance, Ar-Pharazon's mad idea is the kind of thing that realistically speaking has to build on years and years of increasing hubris and paranoia, not something that he comes up with out of nowhere one day. Same with the establishment of Arnor, Gondor and Mordor. But in a television show, if you give it a few seasons even if the in-story timeline has only passed a year or two, that's time enough to make the viewers buy such things.

I think some of their high-level choices are wrong, as discussed here and in other posts - but moving past that, there's plenty I do like and it does have potential to get better. I don't mind the Elves' dialogue being rather formal and stilted - fits with the books and with their general theme of Men and Dwarves resenting the Elves for being so arrogant.