Season 1 - 5/10.
While I didn't really have high hopes, I was still intrigued. The concept of HIMYM was just super fun and you can be quite flexible with your story-telling, so perhaps HIMYF will also give us some interesting episodes.
Unfortunately, immediately in the first episode I realized that this is not it. The show just does not have the charm of its predecessor - there is no Barney, there is no Marshall&Lily, there is no Robin and there is no Ted. The new characters are rather bland and boring and definitely not legen-wait for it-dary. The story-telling is not creative and I find the narrator just annoying who also somehow appears in every episode in contrast to the original show. The jokes never managed to make me laugh and many feel rather forced.
The last episode was not bad, however. Especially the part when Robin appeared (which took me by surprise) was nostalgic and actually quite amusing. But so the best part of HIMYF remains HIMYM. This is not a successful spin-off.