Otis Peak commends itself for the majestic views of Glacier Gorge and Loch Vale that one enjoys from its summit. Otis Peak is located just east of the Continental Divide between Hallett Peak to the north and Taylor Peak to the south. Ascent from the western talus slopes only requires a little scrambling towards the end. This approach is the one followed by the vast majority of those who climb this mountain. One can reach the Continental Divide in the vicinity of Otis from both the north and the south. The distance is about 6 miles either way.
From the north one can climb Flattop Mountain and from there head south, possibly taking a detour to climb Hallett Peak and continuing after Otis to reach Taylor Peak and Powell Peak. A more direct, but considerably more challenging alternative from the north is to climb Chaotic Glacier at the head of trailless Chaos Canyon, situated to the north of Otis Peak. In between the two northern approaches in terms of difficulty is the ascent of Andrews Glacier to Andrews Pass, half a mile to the southwest of Otis Peak. The east ridge offers a Class 2 route to the summit, described in Lisa Foster's Rocky Mountain National Park: The Complete Hiking Guide. With regard to technical climbing, Otis Peak cannot rival its neighbor Hallett Peak for number of routes. Gillett's "High Peaks" guidebook describes some on the towers festooning the south face, but the two main faces--north and south--appear rather "underdeveloped" from the climber's perspective.
Access to Otis Peak is from either the Glacier Gorge trailhead or the Bear Lake trailhead, both in Rocky Mountain National Park. To reach Otis Peak from the north, go to the Bear Lake trailhead and take either the trail for Flattop Mountain or the one for Lake Haiyaha. To reach Otis Peak from the south, go to the Glacier Gorge trailhead, and follow the trail for Mills Lake and the Lock. From Estes Park, drive to the Beaver Meadows entrance to the park. Turn left soon after the entrance gates in the direction of Bear Lake and continue to the well marked trailhead. Instead of driving to the trailhead, you can park at the shuttle bus terminal and board the bus for Bear Lake. Glacier Gorge TH is the second stop, while Bear Lake TH is the third and last stop. Bus schedules are posted at this page. As part of the Bear Lake Road reconstruction, the Glacier Gorge trailhead was moved back by 0.3 mi, thus lengthening the round-trip to Otis Peak from the south by 0.6 mi.
No permits are required for day hikes and climbs in Rocky Mountain National Park. There is no parking fee and the shuttle is free. The entrance pass to the park is $20 per car and is valid for 7 days. The fee, however, is not collected before 6:30 AM. All park visitors should follow the Leave No Trace policy.
When To Climb
Most people climb Otis Peak during the Summer months, though an ascent is possible year-round. The conditions of the glaciers change during the year. During the summer months, an early start is strongly advised to minimize the danger of lightning. (More people are killed in the U.S. each year by lightning than by hurricanes.) An ascent during the winter would be more challenging than one during the summer: One should expect ice, strong winds, sub-zero (Fahrenheit) temperatures, and frequent storms. Spring and Fall present the most variability. Summer conditions may prevail until October, or may be already gone by late August.
There are several camping sites within the park. Details on locations, facilities, reservations, and fees can be found at the camping page of RMNP. Bivy information can also be found on the park's site.
The park's contact information page lists useful numbers. Two webcams, one pointed at Longs Peak and the other at a stretch of the Continental Divide that includes Otis Peak, allow one to get an idea of the conditions. Detailed forecasts are provided by NOAA.
Never forget that the weather may change very rapidly in the high country. The temperature may drop by 50°F or more in a couple of hours. Those who have been caught out by such sudden changes without proper equipment and preparation have not always survived.
Your hunch about the east ridge is correct -- Lisa Foster's guide describes several gullies that provide access, all of which she describes as Class 2. I haven't tried them yet but may do so this summer.