I found very few reviews for Gate 1 Travel and the Monarch Empress traveling the Danube so I thought I would post a quick summary. Marigold252's review in post #2409882 ("Gate 1 17 Day Danube River Cruise with Warsaw, Krakow, Budapest & Prague") on this forum has some fairly detailed additional information.
This was our first river cruise and most of our tour experience has been with various Rick Steves' small group land tours - so our observations about this river cruise come from that perspective.
Gate 1 Travel - Their tag line seems to say it all... "See More of the World for Less". I certainly was unfamiliar with them but many of our fellow cruisers had done numerous land tours with them over the course of 5 - 10 years. They seem pretty well established but have a low profile compared to some of the other river cruise lines. When I compare the quality of the ship, food, service, and experience compared to the many other cruise lines I researched, we certainly felt that it was great value for money.
Ship - The Monarch Empress is quite new (first put into service in 2016 I believe). The decor was more modern/contemporary than what we saw on some of the other ships that were docked close to us. More about clean and sleek and less about overall glitz.
Passengers - Approximately 130 or so passengers for our cruise - a slight majority from the US but Australia, New Zealand, and Canada folks were broadly represented -- with a smattering from other countries as well. The age range was mostly 50 to 80... with just a few folks that were either younger or older than this demographic. Daytime dress was generally casual - this was September so mostly long pants and a mix of layers to adjust for temperature and showers through the day. Dinner dress was a bit mixed. We specifically chose this cruise line over some others because we DIDN'T want to feel pressure to dress up for dinner every night. Men were generally dressed more casually than the women - slacks or dress jeans along with more casual collared/button-down shirts. Women (as expected) dressed up a bit more for dinner/evening... but from my observation the vast majority just tried to add a scarf, a nicer top, and maybe a bit of extra jewelry - though there were a handful of women that (in my opinion looked out of place) dressing in high heels and evening dresses.
Cabin - I used the price difference between Gate 1 and many of the other cruise lines as an opportunity to upgrade to a top-floor "Suite" instead of a mid-level cabin. See the detailed review in the separate section below.
Dining Experience - Because this cruise was more budget conscious, we expected the food to be on the simple/bland side - and we were actually very pleasantly surprised and the variety and quality. I know that some river cruise lines have lots of choices on the dinner menu but we felt that the choices on the Monarch Empress were rich and varied enough to more than meet our needs (and pad our waist lines). With a 4+ course meal (depending on how you counted such things) that was beautifully prepared, we never went hungry. Obviously, if you want to maximize your food experiences than this cruise line might not be a good match... but if you want to try a smaller (but plentiful) array of regional foods and yet have the fall back of some tried & true standbys, I think you will find what was served here to be more than adequate.
Entertainment and Activities - Truthfully, our focus was on the ports and excursions and we took minimal advantage of on-board entertainment/activities. We were generally so tired after being out and about all day that we just wanted to fall in to bed and rest after dinner. My impression is that the on-board activities are probably a bit less sensational than what might be available on other (more expensive) cruise lines -- but in our case why would we want to pay extra for something we never used?
Service - ABSOLUTELY EXCELLENT!! Our minimal experience with ocean cruises prepared us to expect fairly perfunctory service -- but the entire crew made us feel as if we were a part of their family. Within just a day or two the restaurant staff knew many of our specific dining habits - for instance, my desire for a beer instead of wine... it would be delivered to the table within a few seconds of my sitting down anywhere in the restaurant (even though we didn't have assigned seating). The folks that serviced the rooms operated silently in the background - but would address our every need with instant efficiency.
Ports and Shore Excursions - This was a 7 day cruise and we added 2 or 3 days in both Budapest (at the beginning) and in Prague (at the end). We would have loved to spend a bit more time in each of the locations where we stopped -- but this is a challenge for nearly all of the river cruise lines... my research showed that they all had very similar itineraries. In our case we cruised up-stream.... which tends to make actual travel a bit slower. I don't know, however, if this translates into less time at each specific port or whether they simply travel longer at night. Be aware that many of the excursions start relatively early -- Often leaving by 8:15 or 8:30. If you signed up for most/all of the optional excursions (as we did), you may find that you have little time for leisure or taking advantage of after-dinner activities. Most (if not all) of the excursions (standard and optional) had knowledgeable local guides -- but don't expect that you will have the time for a deep-immersion experience... but rather just an introduction with a little time on your own to dig just a bit deeper.
Cabins and Suites are compact on these river cruise lines -- yet I'm a big guy and didn't feel particularly cramped. The extra space in the 210 sq ft suite (vs 170 sq ft for a standard cabin I believe) was given over to a compact but comfortable seating area at the foot of the bed and a more spacious bathroom hosting a double sink and more counter space. Because this is a new ship, LED lighting, plumbing, and heat/AC worked flawlessly and we found no problem storing our clothes or other items. The outer wall is completely given over to a glass wall/french balcony with gorgeous view going by.
BUT... in hind sight I'm not sure that going with the larger suite was worth it... nor paying the up-charge for being on the upper-most deck:
a) With all of the optional excursions that we signed up for, we just found that we were rarely in our cabin unless we were sleeping. We used the nice seating area maybe twice in the entire time.
b) Because we were traveling in September, we found that the weather was typically too cool to leave the french balcony doors open... so we were often in the forward lounge looking at the view. Again... another reason we didn't take full advantage of the room.
c) On the Monarch Empress, I think all of the cabins on the top and middle floors/levels have french balconies regardless of being either a larger suite or smaller cabin... so it MIGHT make sense to just consider the smaller cabin.