We stayed at La Mansion for a week. There are only 22 rooms, so you get very personalized service. The staff and managers knew our name by the second night we were there. Our room was upgraded from standard to a junior suite free of charge. The views of the jungle and the ocean are absolutely breathtaking, especially from the pool and upper deck areas. The manager Robert was especially helpful and friendly.
We booked all our adventure tours through the hotel, which was convenient, but it did come with some hiccups. I paid a deposit for the tours when I booked them through the hotel a month before our stay, but I was then charged the deposit amount again upon checkout. Fortunately, the staff fixed the problem once I emailed them, and my credit card was refunded within a week or two. One more tour issue: the tour guides would always ask for a voucher to prove that we paid in advance, but the front desk staff at the hotel often forgot to give us one (even after we asked). This happened on three occassions, leading to some very frustrated tour guides. Just be sure the hotel staff gives you a voucher!
Other than that, I would highly recommend this hotel. This has the best view of Manuel Antonio's beaches (Playa Biesanz and Playa Espadilla) and the on-site food and ameninties are fantastic.