A good tool chain for annotation is MAKER.

I can ensure you that the N50 value alone is not enough to figure out if your assembly has been good or not.

You can run velvet with different values of kmer using a simple genome (E.coli), and then, you can compare the various kmer-assembled genomes with other trusted genomes using Mauve or Act, and you will be greatly surprised. In my hands, some assembled genomes with higher N50 ended to be worse that other assemblies with lower N50

You don't mention what organism have you used for the assembly. If trusted genomes are there for evaluate, use them before going further

For the genome annotation I would suggest you to give a try to Blast2GO.

For other hand, you can do a gene prediction analysis doing a blast, against protein database or something like that...

But, in the first place, as has been said, you should celebrate ^^

Hope it helps.

Compare it to something(s) else.

Check your original plans for why you decided to sequence in the first place? What were the research questions?

Also, I read a bit more about genome assembly after the original post.

I found that, even though N50 is widely used, or used as a standard, to choose the Kmer size, it doesn't indicate if the genome is assembled correctly. So genome validation becomes an issue.

Following that thought, I found that there are tools for validation, and I only found one: REAPR

Anyone has any experience with that? the manual is a bit hard to follow for some reasons.

Any other tools recommended for assembly validation?

Thanks.

Are you dealing with prokaryote or eukaryote?

Gene annotaiton for prokaryote is well done by PROKKA that uses PRODIGAL for the prediction of CDS.

If your organism belongs to prokaryotes, like mentioned above Prodigal can used for gene prediction. Apart from that, GeneMarkS would also be a good tool.