Why it works as a base
The 1/2/3 and B/C subway lines run straight down the Upper West Side into Midtown and beyond, so you're rarely more than 15–20 minutes from the major landmarks despite being in a residential, less tourist-dense neighborhood. Central Park is a direct walk from most Upper West Side hotels — genuinely closer than from most Midtown ones.
What's around you
The American Museum of Natural History, Lincoln Center, and a strong, unpretentious food scene along Amsterdam and Columbus Avenues that's priced for residents, not tourists. Zabar's, the neighborhood's famous food shop, is worth a visit even if you're not buying groceries.
The trade-off
You're a subway ride, not a walk, from Times Square, the Theater District, and Lower Manhattan — fine for most itineraries, but worth planning around if you want to walk back from a late Broadway show rather than take the train.