The biggest flops were Oz, Sununu not running (although it would still have been winnable for Hassan even with him running), and (so far, at least) Walker, who was always going to be hit or miss. Laxalt is not a "bad candidate" no matter how much people want him to be one (again, NV is a textbook example of generic R vs. generic D), and Masters is still a wild card who is not guaranteed to be the nominee.
Recruitment has been rather awful for the GOP this year - there’s no denying that - but it’s not going to give Democrats a "great" shot at holding the Senate on a night when they’re losing 25 House seats.
The environment would have to improve meaningfully for Dems. As of today, R's are still on track to take the senate even if Walker and Oz both flop. They only need 2 of AZ/NV/NH, all of which are looking pretty good for them.