It's definitely a big change, though you can see the flow of where they were going.   I don't know if I would say it doesn't feel like an Ys game though.  V has much more in common with VI, VII, and the modern remakes than it does with the first 4 games.  If you can accept the modern ones, I think V fits in there.  It's kind of like the missing link between the original style and modern Ys.  I really enjoyed it though, it is definitely short, though not as short as III.  If you know what you're doing and are good you can easily beat III in like 4 - 5 hours.