Every season has something unique to offer at DL. Crowds are quite different than WDW and heavily influenced by local demographics.
Lowest crowds will be when Magic Key's (annual passes) are blocked, particularly the two lowest levels. Also, single day ticket prices are determinative - the higher the single day price, the lower the crowd level. This means that often holidays and weekends are less crowded than weekdays. To complicate things further, this is only true during certain times of the year and other times weekends are more busy. My best advice is to identify the dates with the cheapest single day ticket prices (currently $106) and unblocked MK's and avoid those like the plague (this is why you will see people post about how shocked they are to see Mondays insanely crowded while a weekend wasn't). Another factor - conferences and events like grad nights.
@LKing keeps a running post for 2025 so you can get a sense of when things might be in 2026.
DL also only offers nightly entertainment during parts of the year - summer and winter holidays - and it's otherwise mostly weekends for things like fireworks and Fantasmic. If nighttime entertainment is important to you, then summer is a good bet. Even when offered, fireworks are routinely cancelled for wind at higher elevations, which you won't know about until it happens.
For weather, it's overall much better than Orlando. It is not humid compared to FL and temperatures are more moderate. It doesn't rain during the summer, only on occasion between December-March. Temperatures are warm during the summer, but actually hottest during the fall even though the day to day temperatures are more moderate than summer (extreme heat waves pushing temps over 100 most often occur in Sept and Oct).