This year, general elections will take place in France, Germany, the Netherlands, the Czech Republic, Norway, and New Zealand, and many other nations. The first three of these, as well as the French Presidential election, will be particularly important to watch because of the rise of hardline nationalist parties (FN, AfD, and PVV), a revival of alternative progressive politics (the Dutch Green Party, GroenLinks, is set to receive its best ever results this year having fallen to a low of 4 seats in 2012; it could even finish as high as third), and the continuing failures of the triad of traditional centrist parties (which in Europe belong to the S&D, ALDE, and EPP groups, and which are generally represented by the 3 primary colours of red, yellow, and blue). Current French Presidential polling worrying puts the hardline nationalist and racist Front National and Les Republicanes (formerly UMP) neck and neck on aggregate, with Parti Socialiste lagging in fifth place (behind Front Gauche and En Marche) even though the very disappointing Francois Hollande has stated he will not run for re-election, a historic first in modern French Presidential history. Our Green counterparts, Europe Ecologie-Les Verts, are sadly not to set to perform nearly as well as in Germany or the Netherlands, despite the increasing popularity of environmental initiatives in France.
Meanwhile in the UK, the first 'metro mayor' elections will take place in Greater Manchester, Merseyside (and Halton, not too far from Liverpool), the West of England (the majority of the defunct County of Avon in practice; North Somerset fka Woodspring opted out), Cambridgeshire & Peterborough (nearby Norfolk and Suffolk refused to participate in the devolution deal),
The entirety of Britain will be having council elections (except for those areas not covered by any county council or unitarised county council) as well, with the majority of Scottish councils experiencing substantial boundary changes, and with Welsh councils experiencing them in the next cycle. In 2013, UKIP made 139 gains in county council elections, and its likely collapse (depending on area) this year is set to be a big storyline in county council terms, as are further Green surges and a Liberal Democrat recovery in the South West. Meanwhile, Labour's rural/urban base will likely be hit hard in Cumbria, Derbyshire, Northamptonshire and Nottinghamshire in particular as they fail to properly connect with rural and small town voters under Corbyn's tenure. For some county councils this year could be their very last county council election, as I have stated earlier. For example, as we speak, Buckinghamshire and Dorset County Councils are each preparing to submit a fundamental restructure which will result in the effective abolition of both county councils and their replacement with new unitary authorities.
https://www.mix96.co.uk/news/local/2170789/bucks-councils-want-two-new-councils-to-cover-all-of-the-county/ (latest news on Buckinghamshire plans for new councils)
http://www.bbc.co.uk/news/uk-england-dorset-38206956 (latest news on Dorset plans for new councils)
UPDATE: The Greater Lincolnshire Mayoral election will now not be taking place: http://www.spaldingtoday.co.uk/news/greater-lincolnshire-devolution-deal-is-dead-buried-and-will-not-be-resurrected-1-7730527
UPDATE 2: The Sheffield City Region Mayoral election has been delayed until next year, and might not take place in its proposed form at all: http://www.yorkshirepost.co.uk/news/sheffield-city-region-mayor-election-to-be-delayed-1-8330512