The East and Neck Rivers are in the East River Marsh complex, which I found surprising clear of invasive phragmite reeds that have ruined many of our tidal estuaries. This makes for some excellent bird sightings - several osprey, egrets, more willets than I've ever seen in one place, and two glossy ibises.
There is a tidal current, but I made decent progress against it. I was out for over 3 hours, but it may be possible to paddle far enough upstream to make a good long day of it. You can also access Long Island Sound from this location.
The lower part of the river is in flat level treeless terrain - on a windy day you won't have ocean waves, but you will have ocean winds. I have not been in the river at low tide, but there is a marina that launches smaller powerboats (the RR bridge must be a tight fit for them) upstream of the I-95 bridge.
I suspect that the lower East River is deep enough for canoes and kayaks at any tide.
Here's a link to my blog report on this trip, with photos:
The Guilford town launch may or may not charge for hand-launched boats (some towns in CT wave the boat launch fee for hand launches).