Learn Russian: По-вашему, это хорошая традиция? - In your opinion, is this a good tradition?

Adverbs formed from possessive pronouns using the prefix по- and the ending -ему or -ому are always written with a hyphen. This is a strict spelling rule in Russian for words expressing manner or opinion like по-моему and по-вашему.

Can I just say по вам instead of по-вашему?

No, you need the special adverb form here. The phrase по вам literally means "along you" or "on you". To say "in your opinion," you must use по-вашему for formal or plural "you", and по-твоему for informal "you".

Why is there a comma after По-вашему?

In Russian, introductory words that express a personal opinion or point out the source of information (like по-вашему, по-моему, or кажется) must be separated from the rest of the sentence by a comma.

Since традиция is feminine, why isn't это in the feminine form (эта)?

In this sentence, это is acting as a generic pointing word meaning "this is". When used as a dummy subject to introduce a noun in this way, it always stays in the neuter singular form это, regardless of the gender of the noun that follows.