I had read about the lack of A/C beforehand, and in mid-March it was okay. On the top floor we were able to keep our window open in the evening until we went to bed and we only got a mosquito once, but I imagine they proliferate quickly as the temperature warms. We requested a room fan and that helped keep the room sleepable with the window closed, but I agree the lack of A/C can really catch people off-guard for a Hyatt.
Other than that, the hotel was fine. Definitely shouldn't be going up a category, but given that it was full of tour and convention groups in March, I assume they keep a high cash occupancy rate. Disappointing that it's the only Italian Hyatt without any made-to-order breakfast option, and the mid-quality buffet gets old after a couple days. Probably wouldn't stay here again, but it was a good cost savings for a first longer trip to Venice (before the category increase).