Season 1 was a very solid season on the whole. It wasn't perfect and there were a few episodes that could have been better, namely "A Bum Steer Named Scooby" and "There's a Demon Shark in the Foggy Dark" ("The Ghost that Sacked the Quarterback" also left me with reservations while still not being bad an episode). Having said that, the season did boast some of the show's high points ("High Rise Hair Raiser", "The Harum Scarum Sanitarium", "Watt a Shocking Ghost").
"The Curse of Viking Lake" is a promising start to Season 2. Which to me of the three seasons was the best and most consistent one, despite being the shortest. A few other show high-points in this season too. Did think though that this episode did have potential to be better, to me it is the second weakest episode of Season 2 and did have a few frustrating things. Did say elsewhere 10 years ago that "The Curse of Viking Lake" was a favourite when younger, but that opinion has not held up since. Those frustrating things were outweighed by the many things that "The Curse of Viking Lake" did well.
As usual for Scooby Doo, there is an effective amount of spooky atmosphere. The lake setting is like a character of its own, and while there are certainly animation errors the animation is generally lively and atmosphere with some nicely detailed backgrounds. The music is easy to remember, both the incidental music with some familiar cues and the classic theme song. The script has intrigue and endearingly goofy humour and balances them well.
Furthermore, "The Curse of Viking Lake's" story starts off very promisingly with a creepy opening scene and a first half that has energy, fun and eeriness. The main viking is suitably intimidating and while the gang are all great and Uncle John is likeable in his screen time Shaggy and Scooby are the scene stealers and it is hard to dislike their interaction with the vikings. The voice acting is solid.
However, the second half is not as strong. Personally thought that it did become on the bland and repetitive side. The final solution also underwhelmed me and always did so when younger too. There was never any doubt quite early on who was responsible with suspects being so few, taking away from any suspense.
On top of that, as well as being a pretty old motive for Scooby Doo the villains' plans were muddled and underdeveloped, with it not really being clear why they went to such great lengths when wealthy enough already and who they were targeting. Actually thought the episode would have been effective enough with just one viking, the others didn't serve much point.
In conclusion, promising but with room for improvement. 7/10