We recently stayed at the Marriott Kauai for seven nights. The hotel is just beautiful. The grounds are well-maintained, clean, and lush. The rooms were ok - Marriott standard with no frills. Be prepared - it is a huge property, so yes, you will do some walking. The pool is beautiful and huge - it never felt crowded. Overall the staff is friendly and knowledgeable.
We arrived early and hoped we could check in. No chance. The woman at the desk tried very hard to upsell us to a suite for another $200 per night! After we told her no, she clearly was not interested in finding us a room to check in early. When they say a 4:00 check-in they don't budge - even for Marriott Platinum members.
The resort fee - don't even get me started. Mandatory $25 per night. It includes "free" parking (even though it seems the entire town parks in the lot to use the beach all day), includes "free" internet (although I already get it for free as a platinum member), and a "free" bottle of water in our room every day. Except the cleaning service only left a bottle on three of the seven nights. I am not sure how they justify this added fee.
Food on-property is ok. Breakfast is outrageously, outrageously expensive. $25 for the buffet. If you just want an omelette, juice, and coffee it costs about $23. Just wrong. We ate at Dukes and Cafe Portafino - both quite good. Generally better to eat elsewhere.
Overall we liked the hotel. The resort fee is basically a scam - may make me reconsider staying there again.