Can you please share what you didn't like about it? We've been through the grounds, and they are beautiful. And the pool is fantastic. Is it not heated?
The first half of our trip we stayed at the Westin in Princeville. We just fell in love with the north shore vibe, the resort especially, proximity to things to do, beaches were awsome, etc. It fit us perfectly. Our kids have begged us to take them back and have even told us they would rather go there than WDW again! (And we are currently saving to buy into the Westin vacation program there... we loved it that much!)
The second half of our trip was at the Marriott and I wouldn't recommend it to anyone. The rooms and corridors were institutional, dark, and dreary. It was very old and out of date; it felt closed in and dirty. Our room was really dark to the point where we needed to turn on the lights in the middle of the day and even then it was dark. The pool felt dirty with lots of chipped and stained tiles. It was heated, but felt cold me to anyway; that wasn't a deal breaker for me (I'm just answering your question). I did not use the spa. The service was really lack-luster and the food/drink was so outrageous that we didn't feel like we could sit back and relax. The resort is huge and it took us 15+ minutes to get anywhere on property. Suffice to say it was not a good fit for us, our vacation style, or what we expected.
We had a 1 bedroom "villa" style room. I just looked at the website and I notice now they don't even have pictures of the rooms... so that might tell you something.
The grounds are very nice and the common areas are plentiful. There was one evening our entire family (extended) all grabbed a large table and sat outside and talked for hours. It is in good proximity to everything in Lihue although we spent minimal time in town. Getting to the sights around the island is easy from this location. Kapa'a had a way better shopping area (we are not shoppers), food, and common every day necessities. Kids seemed to enjoy the "big" pool more than the "kids" pool, which was the exact opposite at the Westin where they spent 6+ hours in the kids pool daily. The beds were very comfortable and the room was exceptionally quiet (never heard another neighbor).
This was our second stay at a large Marriott resort and I've determined that how they do "luxury" is not our way of pampering. Our first stay at a large beach resort was the JW Marriott in Cancun and I left not enjoying our stay as much as I had hoped. This second stay in Kauai sealed it that I'm not their type of customer and we don't do large beach resorts well. We won't make that mistake again.
Hopefully that gives a qualification to my remarks (which I realize are pretty harsh). With all that said... we had an amazing trip and the resort didn't take away from our enjoyment of the island even a little bit. But Kauai has sooooo much to offer that the Marriott was not what I would suggest to someone who wants to have a similar magical experience like we had.