NO SPOILERS - check out my review of the prequel episode as well
First episode isn't quite as good as the others in my opinion, and the Engrish can be pretty weird, but it's my favorite show this season. Reasons are below.
First, a brief plot synopsis: time has passed since the events of Fate/Zero, and Waver Velvet is back at it again as the Clock Tower's resident schmuc-- I mean detective!! Okay, in all seriousness, I like this guy. He's intelligent, but a bit too brash and serious for his own good. His companions, including the mysterious hooded Gray and the blonde imouto Reines, round out the main/recurring cast quite well with their own unique personalities, and everyone is always a joy to be around. That may actually work to Waver's detriment, though, since he is usually the one to dispense exposition and thus may come off as a bit trite and one-note, but he has his moments of personality, and they are rather enjoyable. The episode plots aren't bad, but can be a bit trying if you actually want to solve the mysteries yourself; they tend to pull some kind of random magic stuff you can't possibly already know out of freaking nowhere to solve the whole thing. If you're confused by all the fantasy jargon tossed around, don't worry, everyone else is just as confused as you because it's basically all brand spanking new. Did you know the Fate universe had fairies? I didn't, but I should have guessed so! :D :D
Do you need to watch Fate/Zero to enjoy this show? No, in fact you basically need no prior knowledge at all except that the Holy Grail War is this big death game over a wish-granting McGuffin. And even that isn't all that important. Just like this show for what it is, and if you are a Fate fan, then you can appreciate the small bits of fanservice they throw in.
In terms of production, TROYCA have outdone themselves and even ufotable (gasp!), if we're looking at the God-awful UBW series (oh, nvm then). The backgrounds (which I suspect ufotable has been helping with) look gorgeous, the character designs are slick, unique, and memorable, and the CGI, when present, is really solid. This show is probably the best-looking of the season so far. Directing is solid, though I'm not really seeing much in the way of uniqueness. Episode 4 had a cool focus-shifting blur effect, but not much else. The music, courtesy of everyone's favorite Yuki Kajiura is decent (with a solid instrumental opening theme) but it's a noticeable step down from Fate/Zero in my opinion. It doesn't make and carry scenes like it did there.
Should you watch this show? As of yet, it's nothing meaningful, but that could change depending on how Waver is developed; he has the right foundation to be a vehicle for a genuine message. The other characters don't have much in the way of deep themes driving them, so this really is a straight-forward mystery. But, like in my Kabaneri review, the quality of the production is higher than anything else coming out that I am currently watching, so that bumps it from a 7 to an 8.