Overall: C- cruise ship which may be enjoyable if only option based on port of call or schedule, or have low enough expectation. Worst aspects, 1) food; 2) dated feel; 3) NCL seemed to be looking to squeeze money from patrons at every turn; 4) pool area; 5) smoke-filled casino.
The ship is dated to say the least, having been built in 2003. Despite being renovated a few years ago, the Gem was lacking in quality, style, technology and comfort. Compared to many other ships/brands, it is wholly underwhelming, with dark and unappealing public spaces and limited entertainment other than eating/drinking and spending money. The whole experience seemed to be focused on NCL trying to get passengers to spend more once onboard. You couldn't go 10 feet without encountering some way for staff attempting to sell services (more cruises, pictures, artwork, duty free, excursions, etc) or otherwise increase charges (food/drinks, Wi-Fi, casino); it came across as tacky to say the least.
More information / specifics (trip was from Boston to Bermuda in mid-April):