I don't like Obama's politics. I though that he was a bad President on almost all the issues (I guess I was ok in his support of classifying broadband connectivity as a telecommunications service) and that he squandered many opportunities to improve the country by sticking to liberal positions that were largely out-of-touch-with mainstream America.
But I can't say the guy didn't work hard. The Presidency is a hard job, at least when one takes it seriously; his politics aside, he seems to have taken it seriously, which I think is the case for most Presidents. So, if after eight years doing a job that is stressful on the best of days, he now wants to splurge and go on vacation from his vacation, then more power to him.
The criticism by other Democrats is petty and but a thin veil pulled over their actual complaint, which is: "Wah... Obama isn't doing anything to challenge Trump. Wah... Wah... Wah..."