Back when the change from mass rez mercy to valkyrie mercy were announced I was skeptical - I didn’t believe that rez could be balanced as a cool down ability in a way that would be satisfactory.
After playing the new nerfed version I feel that I was wrong. For the first time in 6 months I am really enjoying playing the character again. When Valkyrie was first released - she was way too OP and therefore way too easy to be very fun to play. Even with all the nerfs, untill the most recent, there just wasn’t much you had to think about when playing her. Unlike mass rez mercy you didn’t have to strategise as much, it was super easy to get tempo rez off since they were instant - so you didn’t really have to think much about it. Her mobility was improved which was really fun, but otherwise the play was really dumbed down.
I still played her - but while she was OP there was not alot of option but to play her, and to be honest I played the game alot less during the time that Mercy was OP.
I was very skeptical about the nerf put out late January - I didn’t think it was going to improve playing her at all, actually I thought she was going to be more boring than ever and not really impactful at all. I thought that all the strategy behind the character had been removed, all the tracking of ultimates/positioning/kill feed etc. I was upset that I could no longer use my ult to counter other ultimates or easily swing the fight back to my teams favour.
Actually after playing her for a number of games now I can say I was wrong. The changes made in January were actually very good for the character, and brought back alot of the strategic decision making that she had when she had mass rez - its a bit different now, but actually it is deeper than the mass rez version in my opinion.
I have seen a lot of people say that you can’t use rez in the mid fight or during Valkyrie. This is so dead wrong and if you are only using rez in between fights I can understand how you would find the character very boring, and having no impact. The most important and impactful time to rez is DURING the mid fight - and it is NOT a death sentance.
This is where the old strategising and tracking you had to do with the mass rez Mercy comes back into her game play.
Now you are tracking cool downs, reloads, watching body language, using your own body language to trick the enemy you decided not to go for the rez, tracking ultimates, kill feed, and positioning.
There is honestly nothing more satisfying than rezzing your freshly killed team mate infront of a Mcree who just used his flash bang and has to reload 
As an added bonus - people get tilted when you rez in that kind of situation - they normally tunnel vision in on you and end up dying.
I am actually really enjoying working out if I can rez someone, and working out how I am going to get it off, also working out how important the rez actually is. Yes there are some times when getting a particular team mate back up is MORE IMPORTANT than my own survival and I will go for the rez even if I know I won’t survive it.
Her ultimate is also interesting to use and has alot more options than the old mass rez.
it is very low impact if you miss time it, however used at the right time it is very strong - and it REALLY helps you get a much needed rez off (height advantage + uninterrupted regen). It also gives you fantastic extra mobility that is always useful (also helps for killing pharah).
I can finally enjoy Mercy again, infact, I actually enjoy her more now than mass rez. So I am sorry for doubting you Blizzard - my faith is restored.