The UK introduced the £2 coin not that long ago. In terms of public acceptance it's been successful, although there seem to be supply issues. For example, most of the time when I need >£2<£5 change from the automatic checkout machines in the supermarket, I get a fistful of £1s. Historically, the UK introduction of the 2 shilling piece was successful in the sense that the public liked and used the coin, even though the decimalisation project it was supposed to herald never got off the ground in its original form.
Sweden will be reintroducing the 2 kronor coin next year, albeit in a much changed format from its previous incarnation. It will be interesting to see its progress, but it will be in the context of revising most of the range of coins rather than adding to an established series.
I never really understood the German dislike of the 20 pfennig denomination. It existed fitfully as a silver coin during the Kaiserreich, but then not at all after WW1 (except, as mentioned, in the DDR). I remember ending up with trouser-dropping quantities of 10pf coins because of its lack.